The Monitoring Well, Reflections on Geology & Society
June 14, 2021

Opening Notes and Comments

A few notes before I go on:

I am going to start my blog entries with short comments of issues in geology or science in general.  Today I want to expand on a sentence in my Standard Caveat:

In science, the only authority is the evidence.

In making this statement I want to distinguish between two different meanings of the word science.  The first is the use of the word to mean the scientific method.  The scientific method is a technique to ascertain the truth about something by making observations,  gathering evidence, and then postulating an explanation for the phenomena, based on the evidence.  It works regardless of whatever prejudices you may have, provided you apply the process honestly.

On the hand, Science is a social institution made up of people.  People can be honest or not, selfish or not, open to new ideas or not.  People can have any number of good or bad characteristics.  As an institution, Science will seek to perpetuate its power and privileges.  Geology is no different, and I don't think we can expect it to be any more noble and virtuous than the people who are part of it.  The one thing that should keep our Science in line is a rigid, even religious, adherence to the scientific method.  The alternative is to allow the institution of Geological Science to become museum piece whose best days are behind it. 

Geologists reading this should realise that their choices are part of the ongoing development of the scientific project and that bad choices often have more significant outcomes than good ones.  I think that Shakespeare was right when he had Mark Anthony say this at Julius Caesar's funeral:

                        The evil that men do lives after them;  The good is oft interred with their bones;

Julius Caesar (3.2.82)

If we stick to the scientific method, then the good that we do will outlive us.

A few other notes:

  • My article for the Summer 2021 Keystone Professional is on page 14 of The Keystone Professional which is the quarterly newsletter of Engineers Geoscientists Manitoba.

  • The LinkedIn posting that went viral now has had 439,781 views, 10,901 reactions and 643 comments as of 9:10 AM CDT, June 14, 2021.  I continue to be astonished. 

  • I will bundle up the first six months of my postings into a PDF file that I'll post on this site.  If you want to use it as an introduction to Geology, go ahead, it's free for you to use.  Just give credit where credit is due.

June 14, 2021

Extrusive Igneous Rocks - Part 1

Introduction

While I could go on with many, many other examples of interesting minerals, I think that I've covered the main ones for now.  For the next few postings I will discuss the main types of rocks, starting with extrusive igneous rocks.  However, I will first define some of the terminology starting with the difference between rocks and minerals.

Now, the difference between rocks and minerals is a fairly basic one.  Minerals are naturally occurring solid substances made up of a single chemical compound.   Rocks are generally made up of a suite or collection of minerals, although some rocks are made a single mineral.

What are Igneous Rocks?

Igneous rocks are made from molten rock or magma; in that sense they are the original rocks that made the Earth going back to the Hadean, 4.5 to 3.8 billion years ago, when the Earth was a ball of molten material.  While we have no examples of igneous rocks from the Hadean, except for meteorites, we have igneous rocks from the early Archean to present.

The two main types of igneous rocks are extrusive (also called volcanic rocks) and intrusive rocks (also called plutonic rocks).  In my post of March 8, 2021, I posted the following chart showing a general scheme of classification for igneous rocks:

Figure 1 - General Classification of Igneous Rocks
Credit: Actualist,  Creative Commons Attribution-Share Alike 3.0 Unported license

The main difference between extrusive and intrusive igneous rocks is that extrusive rocks cool and crystallize at or very near the Earth's surface.  On the other hand, intrusive rocks cool and crystallize deeper in the Earth's crust.  Intrusive rocks cool slowly and are made up of coarse to medium sized crystals.  Extrusive rocks cool more rapidly than intrusive rocks and tend to be made of fine crystals. For my discussions, I will include pyroclastic rocks and volcanic glass among extrusive igneous rocks although some classifications treat them as separate.

In this week's post  I'll look at the classification of extrusive rocks. 

Figure 2 - Mt. Etna Making Extrusive Rocks
Credit: U.S. Navy, Creative Commons Attribution 2.0 Generic license.

Extrusive Rock Classification

There is a wide variety of volcanic rock that you can observe in the field.  In an effort to bring some order to the subject, geologists have developed many schemes to classify extrusive igneous rocks.  The International Union of Geological Sciences has proposed two schemes for classifying volcanic rocks:

Figure 3 shows the QAPF classification scheme for volcanic extrusive rocks. 

Figure 3 - QAPF Classification of Volcanic Extrusive Rocks
Credit: Adapted from Definition of qapf diagram, minedat.org 

Figure 4 show the TAS classification scheme for volcanic extrusive rocks.

Figure 4 - TAS Classification of Volcanic Rocks
Adapted from: Le Bas, M. & Streckeisen, A.. (1991). The IUGS systematics of igneous rocks. Journal of The Geological Society - J GEOL SOC. 148. 825-833. 10.1144/gsjgs.148.5.0825 and mindat.org

 In future posts I will discuss the rock types listed above, here are references to the main classifications:

Standard Caveat

The purpose of my weblog postings is to spark people's curiosity in geology.  Don't entirely believe me until you've done your own research and checked the evidence.  If I have sparked your curiosity in the subject of this posting, follow up with some of the links provided here.  If you want to, go out into the field and examine some rocks on your own with the help of a good field guide.  Follow the evidence and make up your own mind.

In science, the only authority is the evidence.

June 7, 2021

Nepheline, Sodalite and other Feldspathoids

Figure 1 - Nepheline
Credit:  Zimbres, Creative Commons Attribution-Share Alike 2.5 Generic license

Feldspathoids such as nepheline, kalsilite, sodalite and leucite are silicate minerals, similar to feldspars, but with lower silica (SiO2) content.  These minerals form in alkali magmas.  Alkaline magmas generally occur on volcanoes associated with oceanic islands and continental rifts.  The rocks formed by alkaline magmas are typically chemically undersaturated with respect to silica; hence they will not contain orthopyroxene and quartz but will have feldspathoid minerals such as nepheline.  Rocks that form from alkaline magmas range in grain size from fine grained basalts to medium grained syenite to coarse grained pegmatites.

So, let's look a few of these minerals

Nepheline and Kalsilite

Figure 2 - KalsiliteCredit: David Hospital,  Creative Commons Attribution-Share Alike 4.0 International license

Nepheline, Na3K(Al4Si4O16), and kalsilite, KAlSiO4, are part of a solid solution series of minerals that vary in the amount of sodium and potassium in the crystal.  Figure 3 is a ternary diagram that shows the relationship between nepheline, kalsilite, leucite, feldspar and silica. The temperature contours are the crystallization temperatures. "R", in the centre, is the reaction point.

Figure 3 - Ternary DiagramAdapted from Fig.143 in Deer, W., R. Howie, & J. Zussman, 1966, Introduction to the Rock Forming Minerals, Longman Group. Ltd., London, U.K.

Nepheline is one of the most common feldspathoid minerals; it is white, grey or yellowish in colour, has a vitreous, greasy lustre, a Moh's hardness of 5½ - 6 and in the hexagonal crystal system.  Kalsilite is similar, it is colourless, white or grey in colour, also has a vitreous, greasy lustre, a Moh's hardness of 6 and is also in the hexagonal crystal system.   Nepheline is much more common than kalsilite and is found in both volcanic and plutonic rocks whereas kalsilite is only found in some volcanic rocks.  One interesting feature of both nepheline and kalsilite is that they form a gel when immersed in strong hydrochloric acid.   

As a commodity, nepheline is sold as nepheline syenite for use in ceramics and glass making.  Major economic deposits of nepheline syenite are in Maine, USA, Baden-Württemberg, Germany and the Kola Peninsula of Russia.

Sodalite

Figure 4 - Sodalite
Credit: Eurico Zimbres,  Creative Commons Attribution-Share Alike 2.5 Generic license.

Although it can come in many colours, sodalite, Na4(Si3Al3)O12Cl, is best known for the specimens that have a striking blue-violet colour.  It has a vitreous to greasy lustre, a Moh's hardness of 5½ - 6 and is in the isometric crystal system.

Sodalite occurs in igneous rocks that crystallized from sodium-rich magmas and is most often found in nepheline syenite, trachyte and phonolite rocks.  It was first identified in rocks from Greenland but has since been found in many other localities, especially in Ontario, Canada.  The most common use for sodalite is as a gemstone.

Leucite

Figure 5 - Leucite in Volcanic Rock
Credit:Kelly Nash,  Creative Commons Attribution 3.0 Unported license.

Leucite, K(AlSi2O6), is white and grey in colour, has a vitreous lustre, a Moh's hardness of 5½ - 6 and is in the tetragonal crystal system. Leucite is found in recent volcanic deposits that are rich in potassium. The type locality is Monte Somma, part of the Somma-Vesuvius Complex near Naples, Italy.  It is also found in the appropriately named Leucite Hills north of Rock Springs, Wyoming, USA.

An interesting feature is that leucite crystallises with a cubic crystal structure at high temperature (ca. 900°C) but reverts to a tetragonal crystal structure upon cooling to 700-600°C.  Also, over time, it can transform into a crystal called pseudoleucite which retains the overall form of the original leucite crystal but is made up of an intergrowth of nepheline and feldspar.  This gradual transformation is why it is only found in recent deposits.

Leucite is used as a gemstone, the principle source of which is Mt. Vesuvius.  Gem quality specimens are apparently quite rare.  It was once used as a fertilizer for its potassium content.

Standard Caveat

The purpose of my weblog postings is to spark people's curiosity in geology.  Don't entirely believe me until you've done your own research and checked the evidence.  If I have sparked your curiosity in the subject of this posting, follow up with some of the links provided here.  If you want to, go out into the field and examine some rocks on your own with the help of a good field guide.  Follow the evidence and make up your own mind.

In science, the only authority is the evidence.

Postscript - The Beer Mug

Core Sample Glass
Credit: Jim Weinpress

Those of you who follow me on LinkedIn might have seen the picture of the beer glass that I posted on that platform.  The credit for the picture goes to Jim Weinpress, Curator of Birds and Mammals at The Virginia Living Museum, Newport News, Virginia.  I grabbed the picture off of a posting that Jim Weinpress made on a Facebook Group called Paleontology Coproliteposting.

As of 9:00 AM CST, June 7, 2021, there have been 311,563 views of the LinkedIn post showing the picture of the beer glass together with 8,190 reactions and 505 comments.  Clearly, this is a good example of a comment that goes viral.

The beer glass is sold by a company called Cognitive Surplus and the beer glass is listed here.

May 31, 2021

Evaporites

"You are the salt of the earth"  Matthew Ch. 5, v. 13.

Figure 1 - Blue Halite, Lanigan Mine, Saskatchewan, Canada
Credit: James St. John, Creative Commons Attribution 2.0 Generic license.

I am going to continue our look at rock forming minerals with a look at evaporites, also known as salts.

Origins of Evaporites

Evaporites originate in the evaporation of sea water.  The salt content of sea water is the result of the erosion of rocks. Physical erosion breaks up rocks into smaller pieces, chemical erosion then dissolves the ions that make up the constituent minerals.  These ions include sodium, calcium, and potassium cations as well as chloride and sulphate anions.   When sea water evaporates, it leaves behind a salt deposit.  Not all dissolved salts have the same solubility.  Depending on the environment, and how often new water enters the system, evaporation of sea water can deposit gypsum/anhydrite (hydrous and anhydrous calcium sulphate), sylvite (potassium chloride) or halite, a.k.a. common salt (sodium chloride).   The halite shown in Figure 1 is from the Middle Devonian Prairie Evaporite Formation; this formation of halite and sylvite was deposited in hyper-saline lagoons on the edge of an interior continental sea.  Similar processes lead to the deposition of gypsum and anhydrite.  Figure 2 shows some of the kinds of environments where evaporites can be deposited.

Figure 2 - Marine Evaporite Depositional Environments
Modified from Figure 15.19 in Nichols, G.
Sedimentology and Stratigraphy, 2009,
Wiley-Blackwell, Oxford U.K.

Extraction of Evaporite Minerals

Halite, sylvite and gypsum/anhydrite are mined from deposits formed in ancient seas.  Sometimes the evaporite deposit contains more than one mineral, so let's look at the extraction methods before looking at the individual minerals.

Mining for halite and sylvite is a common practice.  Ancient salt mines were dangerous places to work and the miners were often slaves. Modern mines are large scale industrial affairs with well paid skilled labour.  The largest underground common salt mine in the world is the Sifto Salt Mine in Goderich, Ontario as in Figure 3.

Figure 3 - Sifto Salt Mine, Goderich ON
Credit: Gordon Leggett,  Creative Commons Attribution-Share Alike 4.0 International license.

Halite and sylvite can also be recovered by the process of solution mining.  In this process, water is pumped down to the salt deposit, the water dissolves salt and is pumped back to the surface.  Solution mining is used to mine sylvite in Saskatchewan; it is also used extensively to recover common salt, halite.

People also produce salt by mimicking the natural processes that lead to salt deposition.  Figure 4 shows the salt production lagoons in the San Francisco Bay.

Figure 4 - Salt Ponds, San Francisco
Credit:Bri, Creative Commons Attribution-Share Alike 4.0 International license.

Gypsum and anhydrite are almost always recovered through open pit mines.  Mining methods are fairly straight forward: remove the overburden and then dig out the gypsum or anhydrite for processing elsewhere.

Not all gypsum comes from mines, however.  Selenite crystals can precipitate out of soils that are rich in sulphates, a phenomena known as desert roses.  When the Red River Floodway was constructed through thick glaciolacustrine clays, selenite crystals were found precipitating out of the clay.  When the Wallace building for the Department of Geological Sciences at the University of Manitoba was completed, they left part of the basement unfinished with exposed clay walls.  In the early 1990's I gave a talk to university students there on working in environmental geology and afterwards, a couple of professors took me into the basement of the building to show me the selenite crystals growing out of the clay walls.

Evaporite Minerals

Common Salt - Halite

Figure 5 - Halite, Trona, San Bernardino Co., California, USA
Credit: Parent GéryCreative Commons  Attribution-Share Alike 3.0 Unported 
 license

Common salt, halite, NaCl, is an everyday commodity and familiar to most people.  The mineral varies in colour and can be colourless, whitish, yellow, red, purple or blue with a vitreous lustre.  Halite has an isometric crystal structure and a hardness of 2.5 on Moh's Hardness Scale.

Salt is an important commodity. The United States Geological Survey (USGS) lists worldwide production figures for salt in 2020 of 270,000 thousand metric tons.  The uses of salt include highway de-icing, industrial chemical production, together with food production and distribution.  Production of salt during 2020 in the United States was: rock salt, 43%; salt in brine, 40%; vacuum pan salt, 10%; and solar salt, 7%.

Libraries of books have been written on the subject of salt.  I found 40,000 entries in a search for "salt" in books on Amazon.ca.  A Google search for "salt" yielded about 809,000,000 results.  If you want to follow up on this subject, there is a deep well of information available.

Sylvite - Potash

Figure 6 - Sylvite, Esterhazy Saskatchewan
Credit: Chris857,  Creative Commons Attribution-Share Alike 3.0 Unported license

Sylvite, KCl, is most commonly mined for potash.  It is typically red in colour with a vitreous lustre.  It has an isometric crystal structure and a hardness of 1.5 to 2 on Moh's Hardness Scale.

Most sylvite is mined from massive evaporite beds, like the Prairie Evaporite Formation, noted above.  The USGS lists worldwide production figures for potash of 43,000 thousand metric tons of K2O equivalent, of which Canada is the largest producer.  The main use for potash is agricultural as a potassium additive to fertilizer.  Potash is also an important additive to glass and is used in the "salt" for water softeners.  If you eat salted sunflower seeds, the sharp salty flavour may come from sylvite added to the salt mix.

An interesting irony is that potash is mostly in demand as a fertilizer component in wet, tropical climates. The major producer in Canada is Saskatchewan, which has a dry, cold, almost sub-arctic, climate.

Gypsum and Anhydrite

Figure 7 - Gypsum, var. selenite
Credit:Géry PARENT, public domain

Gypsum, CaSO4 · 2H2O, and anhydrite, CaSO4, are both varieties of calcium sulphate with gypsum being the hydrous variety.  Both gypsum and anhydrite tend to be found in massive evaporite deposits.  Gypsum seems to be the primary chemical precipitate from sea water.  Following deposition and compaction, anhydrite was formed by the dehydration of gypsum after burial.

Gypsum varies in colour from colourless to white, with occasional tints of other colours due to impurities.  It has a hardness of 2 on Moh's Hardness Scale and has a monoclinic crystal structure.

Anhydrite has a variety of colours including colourless, bluish, blue-grey, violet, burgundy-red, white, rose-pink, brownish, and grey.  It has a hardness of 3 - 3.5 on Moh's Hardness Scale and has an orthorhombic crystal structure

The main use for gypsum and anhydrite is in agriculture and in building materials such as concrete, Plaster of Paris, and drywall.  A typical new home in North America contains more than 7 metric tons of gypsum alone. The USGS lists worldwide production figures for gypsum and anhydrite at 150,000 thousand metric tons. 

The Plaster of Paris that you buy in the hardware store is powdered calcium sulphate,  anhydrite. Mixing the plaster with water turns it into hydrous calcium sulphate,  gypsum.  

Anhydrite and gypsum rock have historically been used as alabaster for building stone and decorative  objects.  For example, the walkways in the Canadian Museum for Human Rights  in Winnipeg are lined with alabaster slabs, as in Figure 8, below.

Figure 8 - Alabaster Lined Walkways at the Canadian Museum for Human Rights
Credit: Intermedichbo - Milorad Dimic M.D.,  Creative Commons Attribution-Share Alike 4.0 International license

Alabaster has also been used to carve bowls and containers.  Figure 9 shows alabaster bowls from ancient Egypt. 

Figure 9 - Alabaster Bowls
Credit:Alensha, Creative Commons Attribution-Share Alike 3.0 Unported licence

Standard Caveat

The purpose of my weblog postings is to spark people's curiosity in geology.  Don't entirely believe me until you've done your own research and checked the evidence.  If I have sparked your curiosity in the subject of this posting, follow up with some of the links provided here.  If you want to, go out into the field and examine some rocks on your own with the help of a good field guide.  Follow the evidence and make up your own mind.

In science, the only authority is the evidence.

May 24, 2021

Carbonate Minerals

Figure 1 - Calcite Under Regular & UV Light
Credit: Didier Descouens,  Creative Commons Attribution-Share Alike 3.0 Unported

We'll continue on with the examination of rock forming minerals associated with sedimentary rocks with a look at carbonate minerals.  Carbonate minerals are the main components of rocks such as limestone, marble and dolomite as well as ore minerals such as Cerrusite (lead carbonate) and Malachite (copper carbonate). 

Many carbonate minerals, especially calcite and aragonite, are precipitated by living creatures either as part of their metabolism, in the case of algae, or to form their shells and structures, in the case of invertebrate animals.  The accumulation of discarded shells, coral structures, and algal precipitates creates limestone rocks.  Diagenesis and metamorphosis of limestone leads to the other carbonate rocks and minerals.  Carbonate rock and minerals can also be the result of chemical weathering and alteration of minerals.

Another interesting feature of carbonate minerals is that they tend to fluoresce under ultraviolet light, as in Figure 1, above.  Figure 2 shows a variety of minerals fluorescing under ultraviolet light.

Figure 2 - Mineral Fluorescence
Credit: Hannes Grobe/AWI - Own work, CC BY-SA 2.5,
https://commons.wikimedia.org/w/index.php?curid=567773

 Calcite and Aragonite

Figure 3 - Aragonite
Credit: Rob LavinskyiRocks.com – CC-BY-SA-3.0

Calcite and aragonite are different crystal forms of calcium carbonate, CaCO3. Both generally originate as chemical and/or biochemical precipitates.  Calcite is the more common form, so we'll look at it first.

Calcite is one of the most widespread minerals on the surface of the earth and originates as a chemical or biochemical precipitate.  It has a trigonal crystal structure, a Moh's Hardness of 3, and is white, yellow or grey in colour.  Calcite effervesces with an acid solution.  Calcite fluoresces under ultraviolet light with a variety of colours from pink to red to blue.

Calcite is the primary mineral in chalk, limestone and marble.  It occurs as a cement in some sandstones and argillaceous rocks such as marl. Chemically precipitated calcite forms rocks such as travertine and the hydrothermal calcite filling in amygdaloid rocks.  Hydrothermal precipitation of calcite can also form sunstone, or Iceland Spar, which is an optically clear calcite that has the ability to polarise light.  This ability to polarise light allowed Icelandic sailors to see the location of the Sun through overcast skies, thus aiding their navigation on the ocean.

Figure 4 - Iceland Spar
Credit:ArniEin,  Creative Commons Attribution-Share Alike 3.0 Unported

Aragonite is generally precipitated from sea water, mostly by living organisms.  It differs from calcite in having a orthorhombic crystal structure.  It is also only metastable. Over time argaonite converts to calcite.  Aragonite is found in the shells of many invertebrates such as molluscs and cephalopods.  In some cases, both aragonite and calcite are found in different layers of the same shell.  Pearls are made out of aragonite.  Aragonite shows yellowish white to pink and occasionally blue or green fluorescence under ultraviolet light.

Dolomite

Figure 5 - Pink Dolomite
Credit: Dlloyd,  GNU Free Documentation License, Version 1.2 

 The term dolomite refers to both the mineral and the rock made of that mineral.  The mineral is named after the Dolomite Mountains in Italy and the French geologist, Déodat Gratet de Dolomieu.

Dolomite, CaMg(CO3)2, is generally light grey, light brown or white in colour although pink examples, like that in Figure 4 are known to occur.  Like calcite, it has a trigonal crystal structure.  The feature that distinguishes calcite from dolomite is that dolomite only weakly effervesces with an acid solution.  Dolomite shows yellowish white to red fluorescence under ultraviolet light.

The mineral dolomite is generally formed by diagenetic changes to limestone after deposition.  In the diagenesis, some of the calcium in the CaCO3 of the calcite is replaced with magnesium, usually through reaction with magnesium compounds carried by groundwater.  The diagenesis of limestone to make dolomite is a huge subject, many books and papers have been written on the subject.  A Googlesearch on dolomite diagenesis returned about 378,000 results, so if this subject interests you, it is a deep rabbit hole of research.

Magnesite

Figure 6 - Magnesite
Credit: Rob LavinskyiRocks.com – CC-BY-SA-3.0

Magnesite, MgCO3, is similar to calcite in that it has a trigonal crystal structure and is dull white or yellow coloured.  Like dolomite, it only weakly effervesces with acid.  Magnesite shows yellowish white to bluish white fluorescence under ultraviolet light.

The distinguishing feature of magnesite is its association.   Magnesite is the alteration product of magnesium rich igneous and metamorphic rocks and is usually found in association with serpentine, talc and/or chlorite rocks.  

Siderite

Figure 7 - SideriteCredit: Géry PARENT, public domain

An iron ore mineral, siderite, FeCO3, is a various shades of yellow and brown in colour.  It most commonly occurs in bedded sedimentary rocks and appears to be the result of the weathering of carbonate in the presence of dissolved iron. 

Malachite and Azurite

Figure 8 - Azurite on MalachiteCredit:Marie-Lan Taÿ Pamart,  Creative Commons Attribution 4.0 International

 Malachite, Cu2(CO3)(OH)2, and Azurite, Cu3(CO3)2(OH)2, are both copper carbonates and important copper ores.  Malachite is bright green in colour and azurite is blue.  Both are found as secondary minerals formed by the chemical weathering of copper bearing minerals, such as chalcopyrite, by dissolved carbon dioxide in water.

In addition to their use as copper ores, some specimens of malachite and azurite are used as gemstones.  Malachite is also used as a stable green pigment for paints.

Cerrusite

Figure 9 - Cerrusite
Credit: Rob LavinskyiRocks.com – CC-BY-SA-3.0

 Cerrusite, PbCO3, is a lead carbonate used as a lead ore.  Clear, white, gray, blue, or green in colour.  Cerrusite fluoresces yellow and yellowish white under ultraviolet light.  It is another mineral formed by weathering, in this case the weathering of minerals containing lead like galena.

Rhodochrosite

Figure 10 - Rhodochrosite and Quartz
redit: Rob LavinskyiRocks.com – CC-BY-SA-3.0

A manganese carbonate, rhodochrosite, MnCO3, is typically pink in colour.  Rhodochrosite fluoresces red under ultraviolet light.

Rhodochrosite is often formed by high temperature alteration, metasomatism, of manganese rich minerals and it found in association with other manganese minerals such as rhodonite and spessartine.  It also occurs in hydrothermal veins and in some pegmatites.   Rhodochrosite is best known as a gem mineral.  

More Carbonate Minerals

Other carbonate minerals that might be of interest include:

·         Ankerite, Ca(Fe2+,Mg)(CO3)2,

·         Huntite, CaMg3(CO3)4,

·         Smithsonite, ZnCO3,

·         Strontianite, SrCO3 , and

·         Witherite, BaCO3

Most of these minerals occur as the result of  hydrothermal alteration of other minerals.

Standard Caveat

The purpose of my weblog postings is to spark people's curiosity in geology.  Don't entirely believe me until you've done your own research and checked the evidence.  If I have sparked your curiosity in the subject of this posting, follow up with some of the links provided here.  If you want to, go out into the field and examine some rocks on your own with the help of a good field guide.  Follow the evidence and make up your own mind.

In science, the only authority is the evidence. 

May 17, 2021

Clay Minerals

Figure 1 - Ming Vase
Credit: Gary Todd,  Creative Commons CC0 1.0 Universal Public Domain Dedication

You might be thinking:  What does a Ming Vase have to do with a blog on geology?  The simple answer is that while clay minerals are complex and fascinating, they are often dull and not very pretty.  However, clay can be made into beautiful things.

Weathering - Where Clay Minerals Come From

Unlike the other rock forming minerals that I've discussed in this blog, clay minerals were not created in the heat and pressure that gave us the minerals in igneous and metamorphic rocks.  Clay minerals, along with sand and carbonate minerals, are the result of weathering processes that took place under the temperatures and pressures we have at the Earth's surface. Burial and compression of clay deposits create mudstones and shales, however the clay minerals themselves are the product of surficial weathering.

Weathering of rocks can be broken down into two main processes: physical weathering and chemical weathering.  Physical weathering is the breakdown of rocks by forces such as water erosion, wind erosion, biological action, frost fracturing, and heat stress fracturing.  Chemical erosion begins with the simple fact that carbon dioxide dissolved in rain water is slightly acidic.  this slight acidity, a pH just under the neutral pH of 7, will gradually dissolve minerals.  the chemical excretions of living things can also cause chemical weathering.

Some minerals are more susceptible to weathering than others.  The relative chemical stability of minerals was discovered by Norman Bowen when he investigated the melting and crystallization of igneous rocks. Originally published in 1928, as The Evolution of the Igneous Rocks (Anniversary Edition, 1956,  Dover Publications, New York) Bowen's work showed a definite pattern of crystallization of minerals out of a magma now called the Bowen Reaction Series.  Research by Samuel S. Goldich, originally published in The Journal of Geology, Vol. 46, No. 1, Jan. - Feb. 1938 (behind a pay wall), showed a pattern in the weathering of the minerals that mirrored Bowen Reaction Series, this weathering pattern is now called the Goldich Dissolution Series.  In the Goldich Dissolution Series, the minerals at the top of the Bowen's Reaction Series, such as olivine and calcium rich plagioclase, are the first to weather whereas the minerals near the bottom, the minerals with the lowest melting point, are the most resilient to weathering.  The explanation is due to their chemistry: the ionic bonds in the minerals most likely to weather are weaker than those in the more resilient minerals.  Combining the two series, we get the diagram shown in Figure 2.

Figure 2 - Combined Bowen Reaction Series
& Goldich Dissolution Series (by author)

Clay Mineral Structure

Clay minerals are similar to mica in that they are sheet silicates.  In case of clay minerals, they are made up of hydrous aluminium sheet silicates containing variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations.   The key is the water (the hydrous bit), clay minerals bind up water in their crystal matrix, as in Figure 3.

Figure 3 - Atomic Structure of Montmorillonite ClayCredit:   Andreas Trepte,  Creative Commons Attribution-Share Alike 2.5 Generic

Common Clay Minerals

Kaolinite

                                    Figure 4 - Kaolinite                                                          Figure 5 - Kaolinite Atomic Structure
Credit:  USGS Minerals and Materials Photo Gallery,       Credit: Kent G. Budge,  Creative Commons CC0 1.0                                       public domain                                                                                 Universal Public Domain Dedication

Named after the type locality,  Gaoling Mine in China, Kaolinite, Al2(Si2O5)(OH)4, is generally white, but can also have red, brown or bluish tints.  Kaolinite is formed from the hydrothermal alteration of feldspars, feldspathoids and other silicates under slightly acidic conditions.  Kaolinite  is usually found in massive deposits of the mineral.  Kaolinite is one of the most important clay minerals for pottery production, especially for white coloured pottery such as fine china.

Illite

                                               Figure 6 - Illite                                                               Figure 7 - Illite Structure                Credit: Mindat.org, Creative Commons                                        Credit:  USGS, public domain
                                Attribution 3.0 Unported

Illite, K0.65Al2.0[Al0.65Si3.35O10](OH)2, is a pale coloured mineral, varying from gray-white to silvery-white to greenish-gray.  It is the dominant mineral in shales and mudstones.  Illite is derived from the weathering of feldspars and other silicates under alkaline conditions.  The structure of illite resembles that of mica and is considered a variety of muscovite for that reason.  

Illite is named after Illinois, where the type locality, the Maquoketa Shale is found.

Montmorillonite

Figure 8 - Brushite-MontmorilloniteCredit: Leon Hupperichs, Creative Commons Attribution-Share Alike 3.0 Unported

Also called smectite,  montmorillonite, (Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2 · nH2O, varies in colour from white to buff to yellow to green and sometimes pale pink to red.  It is formed by the alteration of volcanic rocks such as tuff and volcanic ash.  Montmorillonite is the principle component of bentonite.  Montmorillonite was named after the type locality in Montmorillon, France.

Vermiculite

Figure 9 - VermiculiteUSGS Minerals and Materials Photo Gallery, public domain

Vermiculite,Mg0.7(Mg,Fe,Al)6(Si,Al)8O20(OH)4 · 8H2O,  can occur in the contact between felsic intrusive rocks and mafic or ultramafic rocks or it can be formed by the hydrothermal alteration or weathering of biotite. Yellow, green and/or brown in colour, it forms worm-like structures when heated up, hence the name. 

Uses of Clay

The United States Geological Survey Mineral Commodity Summaries 2020 lists the following kinds of clay produced or imported into the United States:

  • Ball clay

  • Common clay

  • Bentonite

  • Fuller’s earth

  • Fire clay

  • Kaolin

Ball clay and common clay are used to make such items as porcelain, floor and wall tiles and sanitary-ware (toilets, urinals and sinks).  Bentonite is used mostly for kitty litter and drilling mud.  Fuller's earth is a form of montmorillonite clay used in textile production,  decontamination, food production (look for aluminum silicate on the ingredients label) and cosmetic clay.  Fire clay is used to make cement and refractory brick.  Kaolin is used in the production of fine porcelain and to make glossy white paper.

Vermiculite, noted above, is best known for its use as insulation.  Natural occurrences of vermiculite in nature usually have a small amount of asbestos.  Inhaling asbestos fibres can lead to mesothelioma, usually around 30 years after the initial exposure.  If you have vermiculite insulation in your attic, don't mess around with it unless you are wearing the proper personal protective equipment (PPE).

Further Studies

I have barely scratched the surface in discussing clay minerals; there is an immense body of knowledge on the subject of clay minerals.  Some geologists spend their whole career studying them. 

If the subject interests you, Internet searches alone into clay and clay minerals can lead you deep into a rabbit hole of published scientific investigations.  There is also The Clay Mineral Society with an accompanying Clays and Clay Minerals journal. 

Or you can just be a child again, and play in the mud.

Standard Caveat

The purpose of my weblog postings is to spark people's curiosity in geology.  Don't entirely believe me until you've done your own research and checked the evidence.  If I have sparked your curiosity in the subject of this posting, follow up with some of the links provided here.  If you want to, go out into the field and examine some rocks on your own with the help of a good field guide.  Follow the evidence and make up your own mind.

In science, the only authority is the evidence.

May 10, 2021

Olivine

Figure 1 - Olivine in Thin Section
Credit: only_point_five"Olivine" by only_point_five is licensed under CC BY-NC 2.0

 Olivine is an important rock forming mineral.  It is also interesting in its own right.  The Olivine Group includes the Fayalite-Forsterite Series, Monticellite, Kirschsteinite, Tephroite, and Knebelite.  The most common examples of olivine are found in the Fayalite-Forsterite Series, a solid solution series of iron-magnesium silicates.  Replacing the iron and magnesium cations in the atomic matrix with calcium or manganese will make the other olivine minerals.

The distinguishing characteristics of olivine is its olive green colour, its orthorhombic crystal shape and moderate to imperfect cleavage. 

Olivine minerals are typically found in dunite, peridotite, gabbro, dolerite, basalt and syenite, but can also be found in sediments that have been thermally metamorphosed through contact with an igneous intrusion.  It is when rocks have been thermally metamorphosed that the iron and magnesium in Fayalite-Forsterite olivine can be replaced with calcium or manganese.  Figure 2, below, graphically shows how thermally metamorphosis works.

Figure 2 - Thermal MetamorphosisCredit: Jasmin Ros, Creative Commons Attribution-Share Alike 3.0 Unported

 Much of the Earth's mantle is made up of olivine and olivine is also found in some meteorites.  Researchers Michael J. Russell and Adrian Ponce listed olivine as one of the "Six ‘Must-Have’ Minerals for Life’s Emergence".

Chemistry and Structure

The general chemical formula for olivine is

A2SiO4

Where A is a cation such as iron (Fe 2+), magnesium (Mg 2+) calcium (Ca) or Manganese (Mn) and  SiO4 4–  is the silicate anion.

The general description of the structure of olivine is orthosilicate.  The silicate anion forms a tetrahedron that is not directly linked to other silicate tetrahedrons.  Rather, the tetrahedrons are linked by the cations, as in Figure 3.

Figure 3 - Atomic Structure of OlivineCredit: andreww , Public Domain

Olivine Minerals

Fayalite-Forsterite Series

Figure 4 - OlivineCredit: Aram Dulyan, Public Domain

The classic olivine minerals are those that are part of the Fayalite-Forsterite Series. Fayalite, Fe2SiO4, and forsterite, Mg2SiO4, form a solid solution series.  Figure 5, below, shows a phase diagram for the Fayalite-Forsterite Series.

Figure 5 - Forsterite-Fayalite SeriesModified from Binary Phase Diagrams

Pure examples of forsterite are rare in nature, almost always there is a mixture or iron and magnesium in the crystal matrix.  This is usually expressed as the forsterite percentage: the abbreviation Fo75 means that the olivine is 75% forsterite.  Olivine that leans toward the forsterite composition, Fo92 and Fo88, is found in dunite and peridotite.  Gabbro, dolerite, basalt, and trachyte often contain olivine in the Fo85 to Fo40 range.

Iron rich olivine and relatively pure fayalite are found in dolerite , ferrogabbro, granophyre and syenite rocks.  Fayalite also occurs in iron rich sediments that have been thermally metamorphosed.

Fayalite is named after the Island of Faial in the Azores.  Forsterite is named after Johann R. Forster, a German scientist and explorer.

Monticellite

Figure 6 - Monticellite Crystals on Brown Vesuvianite
Credit:
Robert M. Lavinsky, iRocks.com – CC-BY-SA-3.0

Named after the Italian geologist Teodoro Monticelli, Monticellite,CaMgSiO4, is a gray to colourless mineral.  It is most commonly found in thermally metamorphosed rocks at the contacts between volcanic rocks and siliceous dolomitic limestone.  

Kirschsteinite

 Figure 7 - Kirschsteinite
Credit: Leon Hupperichs, Creative Commons Attribution-Share Alike 3.0 Unported

Kirschsteinite, CaFe2+SiO4, is a greenish grey olivine mineral where calcium has been incorporated into the crystal matrix.  It is typically found in calcareous skarn, another thermally metamorphosed rock formed in the contact between intrusive volcanic rock and limestone sedimentary rock. Kirschsteinite was named after the German geologist Dr. Egon Baron von Kirschstein, best known for a disastrous 1908 expedition to Mount Karisimbi on the border between Rwanda and the Democratic Republic of the Congo.

Tephroite and Knebelite

Figure 8 - Tephroite
Credit: Robert M. Lavinsky,  iRocks.com – CC-BY-SA-3.0

Varying in colour from grey, to olive-green, to flesh red or reddish-brown, to dark brown and black, Tephroite, Mn2SiO4, and closely related Knebelite, (Mn Fe)2SiO4, are formed where manganese is incorporated into fayalite.  These two minerals are also found skarns formed in the contact between intrusive volcanic rock and iron-manganese ores.

Tephroite was named by Johann Friedrich August Breithaupt for its colour, from the Greek τεφροζ "tephros" = ash-coloured.  Knebelite was named after a German poet and translator, Karl Ludwig von Knebel.

Olivine as Jewelry

Figure 9 - Swarovski Tennis Bracelet in Olivine
Credit: Mannia&Titta licensed under CC BY-ND 2.0

Olivine is best known as the jewel Peridot.   Peridot serves as a birthstone for the month of August.  The most valuable Peridot crystals are dark green or lime green and are relatively clear.  Gem quality olivine tends to be on the Forsterite end of the Forsterite-Fayalite Series.

Standard Caveat

The purpose of my weblog postings is to spark people's curiosity in geology.  Don't entirely believe me until you've done your own research and checked the evidence.  If I have sparked your curiosity in the subject of this posting, follow up with some of the links provided here.  If you want to, go out into the field and examine some rocks on your own with the help of a good field guide.  Follow the evidence and make up your own mind.

In science, the only authority is the evidence.

May 3, 2021

Amphiboles

Figure 1 - Amphibole in Thin Section
Credit:"Amphibole" by ZEISS Microscopy is licensed under CC BY-NC-ND 2.0

Amphiboles form a large group of chain silicate minerals.  Approximately 100 minerals have been identified within the amphibole group.  Generally, amphiboles are found in coarse grained plutonic rocks and in a variety of metamorphic rocks formed under conditions ranging from the blueschist to the greenschist and to the granulite  facies  Figure 2 illustrates the various facies in metamorphic rocks, the depths, temperatures and pressures in the diagram refer to the conditions under which the minerals were formed.

Figure 2 - Metamorphic Facies
Credit: David Magrass, Public Domain, Wikimedia Commons

All minerals in the  amphibole group are characterized by perfect cleavage in two directions and a splintery fracture. Colours are typically dark green, brown or black.  However, they can also be colorless, white, yellow, green, blue, and even lilac.  One distinguishing feature of amphiboles is a parallelogram cross-section when seen in thin section, Figure 1, above, is a good example.

Chemistry and Structure

The general chemical formula for amphiboles is as follows:

X2-3Y5Z8022(OH)2

Where:            X is Ca, Na, K, Mg

                             Y is Mg, Fe2+, Fe3+, Al, Ti, Mn, Cr, Li, Zn

and where      Z is Si, Al

The silica tetrahedra in amphiboles form double chains, as in Figure 3

Figure 3 - Amphibole Silica Tetrahedra
Credit: Steven Earle, Creative Commons Attribution 4.0 International License,
Chapter 2.4 of Physical Geology

The other ions (Ca, Na, K, Mg, Mg, Fe2+, Fe3+, Al, Ti, Mn, Cr, Li, Zn) will be found in the interstices between the tetrahedra.  This structure allows for a wide variety of chemical formulae, thus the 100 different minerals in the amphibole group.

Common Amphibole Minerals

Common minerals within the amphibole group include: the ferro-actinoliteactinolitetremolite series, hornblende, anthophyllite, cummingtonite, arfvedsonite, glaucophane, and riebeckite.  Let's look at them separately.

Ferro-Actinolite Actinolite Tremolite Series

Figure 4 - Actinolite                                                 Figure 5 - Tremolite
Credit: P.Fernandes (Trebaruna),                         Credit: John Sobolewski,
Creative Commons Attribution 3.0 Unported                             Creative Commons Attribution 3.0 Unported

Ferro-actinolite(Ca2Fe2+5(Si8O22)OH2), actinolite (Ca2(Mg4Fe)(Si8O22)(OH)2) and tremolite (Ca2(Mg5)(Si8O22)(OH)2) are closely related minerals and form a solid solution series, as in Figure 6:

Figure 6 - Tremolite - Actinolite SeriesCredit: Gina Lee Barnes, ResearchGate

Actinolite is typically green in colour, ferro-actinolite ranges from colourless to green to black and tremolite ranges from colourless to grey.  Tremolite and actinolite occur in metamorphic rocks, either metamorphosed carbonate rocks or metamorphosed ultramafic rocks.  Actinolite is the diagnostic mineral of the greenschist metamorphic facies.  Nephrite, a type of jade, is a form of tremolite-actinolite.

Hornblende

Figure 7 - HornblendeCredit: Creator:Robert Lavinsky,  Creative Commons Attribution-Share Alike 3.0 Unported

Hornblendes are another series that vary from magnesio-hornblende, Ca2(Mg4Al)(AlSi7O22)(OH)2, to pargasite,NaCa2(Mg4Al)(Al2Si6O22)(OH)2. Hornblende varieties tend to be black but also occur in various shades of green.  It is one of the most common minerals in regionally metamorphosed rocks and is also common in granites and intermediate plutonic rocks.

Anthophyllite

Figure 8 - AnthophylliteCredit: Ra'ike,  GNU Free Documentation License

Anthophyllite, Mg2(Mg5)(Si8O22)(OH)2, varies in colour from white to brown and green and is found in metamorphic rocks such as gneisses and anthophyllite-talc schists.

Cummingtonite

Figure 9 - Cummingtonite, Dannemora Mine, Uppsala, Sweden
Credit: 
Hannes Osterhammer Creative Commons Attribution-Share Alike 3.0 Unported

Cummingtonite, Mg2(Mg5)(Si8O22)(OH)2 occurs as light brown to green aggregates of fibrous crystals.  It is found in amphibolites, which are regionally metamorphosed mafic igneous rocks.  Cummingtonite is also found in igneous rocks such as dacite. 

Arfvedsonite

Figure 10 - Arfvedsonite
Credit: Leonardo Cianchi, Public Domain

Arfvedsonite, Na3(Fe,Mg)4FeSi8O22(OH)2, is another dark coloured amphibole ranging from black to green. It is characteristic of alkaline plutonic rocks and such as nepheline-syenite.

Glaucophane and Riebeckite

Figure 11 - Glaucophane                                                              Figure 12 - Crocidolite Riebeckite   
Credit: Erik Vercammen,                                                                   Credit: Siim Sepp(Sandatlas)
Creative Commons Attribution 3.0 Unported              Creative Commons Attribution-Share Alike 3.0 Unported

Glaucophane, Na2(Mg3Al2)(Si8O22)(OH)2, and riebeckite, Na2(Fe2+3Fe3+2)(Si8O22)(OH)2 also form an amphibole series.  These two minerals are dark green to dark blue to black in colour.  Glaucophane occurs in metamorphic rocks associated with folded geosyncline terraines such as amphibolites and greenschists.  Riebeckite, on the other hand, occurs in igneous rocks such as granite and syenite.  Crocidolite, a kind of asbestos, is a form of riebeckite.

Standard Caveat

The purpose of my weblog postings is to spark people's curiosity in geology.  Don't entirely believe me until you've done your own research and checked the evidence.  If I have sparked your curiosity in the subject of this posting, follow up with some of the links provided here.  If you want to, go out into the field and examine some rocks on your own with the help of a good field guide.  Follow the evidence and make up your own mind.

In science, the only authority is the evidence.

April 26, 2021

Pyroxene Group


Figure 1 - Pyroxene CrystalCredit: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0

Unless you are a geologist or are familiar with geology you may not have heard about the pyroxene group of minerals.  However, they an important and widespread group of minerals found in many igneous and metamorphic rocks.  Among aggregate rocks used for construction materials , dark coloured(mafic) rocks called trap rocks are rich in pyroxene minerals.

To put their importance into context, Figure 2 shows the relative abundance of various rock forming minerals, pyroxenes make up around 11% of the minerals in the Earth's crust.


Figure 2 - Mineral Abundance

Characteristics of Pyroxenes

Pyroxene are considered "chain silicate" minerals.  Figure 3, shows the crystal structure of pyroxenes

Figure 3 - Crystal Structure of Pyroxene
Credit:
 American Mineralogist Crystal Structure Database

Pyroxenes are commonly divided into two subgroups:  clinopyroxenes and orthopyroxenes subgroup.  Clinopyroxenes show monoclinic crystals whereas orthopyroxenes have orthorhombic crystals. 

Chemically, pyroxenes have the following general chemical formula:

ABC2O6

·         Where A can be one or more of the following: Ca, Na, Fe++, Mg, Zn, Mn, or Li;

·         Where B can be one or more of the following: Mg, Fe+++, Fe++, Cr, Al, Co, Mn, Sc, Ti, or Vn; and

·         Where C can be Si, Al, or a combination of both

Many cation substitutions can occur in the A and B positions.

Figure 4, is a ternary diagram showing the relationship between various types of pyroxene

Figure 4 - Ternary Diagram, Pyroxene Group
Credit: Wiring Diagrams Free

Table 1, below, lists the pyroxene minerals and their chemical compositions

Table 1 - Pyroxene Minerals

Common Pyroxenes and their Occurrence

Spodumene - LiAl(SiO3)2

Figure 5 - Spodumene
Credit: Rob Lavinsky, 
iRocks.com – CC-BY-SA-3.0

Found mostly in granitic pegmatites, spodumene is an ore of lithium.  Some varieties of spodumene are gemstones; pink to purple spodumene is known as kunzite, green spodumene is known as hiddenite, and yellow spodumene is known as triphane.

Jadeite - Na(Al,Fe+++)Si2O6

Figure 6 - Jadeite from Burma
Credit:
Jsj1771Creative Commons Attribution-Share Alike 3.0 Unported

Jadeite comes in many colours including green, greenish white, purplish blue, blue-green, violet, white and black.  Jadeite is famous for its use in jewelry and ornamentation.  It is also a tough, resilient mineral that resists fracturing and was used for stone axes in the Neolithic.  Jadeite is typically found in metamorphic rocks, especially in glaucophane schists.

Diopside - CaMgSi2O6

Figure 7 - Faceted Diopside
Credit:
Didier Descouens,  Creative Commons Attribution-Share Alike 4.0 International

Another green coloured pyroxene, diopside is one of the most common members of the pyroxene group. It often occurs as generally pale greenish to greyish green crystals in metamorphosed limestones (marbles).  It is mostly used for jewelry.

Enstatite - Mg2Si2O6

Figure 8 - Enstatite
Credit:
Rob Lavinsky, iRocks.com – CC-BY-SA-3.0

Found in magmatic mafic rocks, enstatite (also called clinoenstatite) is generally olive green to brown in colour, occasionally white or yellow.  Enstatite is occasionally used as a gemstone called bronzite.

Augite - (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6

Figure 9 - Augite in Thin Section
Credit:
Strekeisen, Creative Commons Attribution-Share Alike 4.0 International

A major subgroup within the clinopyroxenes, augite varies in proportions of Ca, Mg, and Fe.  The colour of augite also varies and includes Brown-green, black, green-black, brown, and purplish brown.  It is a major rock forming mineral found in mafic igneous rocks, ultramafic rocks, and some high-grade metamorphic rocks. It is one of the few minerals that has no commercial use.

Pigeonite, (Ca,Mg,Fe)(Mg,Fe)Si2O6

Figure 10 - Pigeonite in Thin Section
Credit: user:Omphacite, Public domain, via Wikimedia Commons

Named for the type locality of Pigeon Point, Minnesota, pigeonite varies in colour from black to brown to greenish brown. It is it is mostly found in igneous rocks like basalts and dolerite.

Hedenbergite - CaFe++Si2O6

Figure 11 - Hedenbergite
Credit:
Robert M. Lavinsky,  Creative Commons Attribution-Share Alike 3.0 Unported

Hedenbergite is a brown to black clinopyroxene found in a variety of environments including metamorphosed iron formations, iron-magnesium skarns, granites, and as xenoliths in kimberlite.

Wollastonite - Ca2Si2O6

Figure 12 - Wollastonite
Credit:
AyselkaDjabrailova,  Creative Commons Attribution-Share Alike 4.0 International

At the top of the ternary diagram in figure 4 is a mineral called Wollastonite.  While not generally considered a member of the pyroxene group, I am including it here because it is so often shown in the ternary diagrams that illustrate the chemistry of pyroxene.  Wollastonite is a light coloured (felsic) mineral: white, gray-white, light green, pinkish, brown, red, and yellow.  It is found in igneous rocks, in metamorphic siliceous carbonates rocks, and as a skarn deposit.  Among others, wollastonite is used in ceramics, for brakes and clutches, metal refining, as a paint filler, and in plastics.

Standard Caveat

The purpose of my weblog postings is to spark people's curiosity in geology.  Don't entirely believe me until you've done your own research and checked the evidence.  If I have sparked your curiosity in the subject of this posting, follow up with some of the links provided here.  If you want to, go out into the field and examine some rocks on your own with the help of a good field guide.  Follow the evidence and make up your own mind.

In science, the only authority is the evidence.

April 19, 2021

Mica

Figure 1 - Mica
Credit: B. Domangue, licensed under the Creative Commons Attribution-Share Alike 4.0 International

Continuing on with the theme of rock forming minerals, this week we'll look at mica.  Mica is a general term for a number of minerals with similar characteristics.  The term mica was first recorded in 1706 as smicka, which seems to have been taken from the Latin word micare - to twinkle, flash or glisten - an allusion to the pearly lustre of the separated sheets.

General Characteristics

All micas are sheet silicates and form monoclinic crystals that cleave along parallel planes.  The sheets that form along the cleavage planes show a vitreous, silky or pearly lustre.  The hardness of micas generally vary from 2½ to 6 on Moh's Hardness Scale.  With mica, the hardness of the flat sheets along the cleavage planes is lower, i.e. 2 - 3 while the hardness of the crystal edges is in the higher range.

The main varieties of mica are: muscovite, paragonite, glauconite, lepidolite, phlogopite, biotite, zinnwaldite, margarite, and clintonite. The full list of minerals in the mica group are found here.

Figure 2 shows the general molecular structure of one variety of mica, muscovite.  Variations on this general structure are characteristic of mica minerals.

Figure 2 - Muscovite Mica Structure
Credit: Zhifeng Shao, Researchgate

Main Types of Mica

Muscovite

With a chemical formula of KAl2(AlSi3O10)(OH)2, muscovite is generally white to colorless and has a vitreous, silky, pearly lustre.  It is found in a wide variety of geological environments, but especially in pegmatite.  It has been used as an electrical insulator, a heat resistant transparent "glass" on wood fired stoves or lamps, and as a "glitter" additive to paint.  Large crystals in pegmatite rock found in Russia, i.e. ancient Muscovy, used to be called Muscovy Glass.

Paragonite

Paragonite has a crystal formula of NaAl2(AlSi3O10)(OH)2 and is generally colourless to pale yellow. It occurs in schists and phyllites, in muscovite-biotite gneisses, quartz veins, in fine-grained sediments, and glaucophane bearing rocks.

Glauconite

Also called greensand, glauconite has a chemical formula of (K,Na)(Fe3+,Al,Mg)2(Si,Al)4O10(OH)2. As the alternate name suggests, glauconite is generally green in colour, ranging from blue green to yellow green.  Glauconite is a common additive to fertilizer for its potassium content.  It is found in marine sediments.

Lepidolite

With a chemical formula of KLi2Al(Si4O10)(F,OH)2 to K(Li1.5Al1.5)(AlSi3O10)(F,OH)2, lepidolite is generally pink, light purple or light rose red.  It is a minor ore of lithium and is sometimes used in jewelry.  Lepidolite is found in granite pegmatite rocks.

Phlogopite

Phlogopite ranges in colour and can be brown, gray, green, yellow, or reddish brown. The chemical formula for phlogopite is KMg3(AlSi3O10)(OH)2.  Phlogopite is generally found in metamorphosed limestone and ultrabasic rocks.

Biotite

A very common dark coloured iron rich mica, biotite has the general chemical formula of K(Mg,Fe)3AlSi3O10(OH)2.  Biotite was named after the French physicist and mineralogist, Jean-Baptiste Biot [April 21, 1774 - February 3, 1862], who studied the optical properties of mica. It is found in a variety of geological environments ranging from igneous to metamorphic and is one of the most common kind of mica you are likely to find in the field.

Zinnwaldite

Named after Zinnwald, on the border between Germany and the Czech Republic, zinnwaldite is a brown mica found associated with the tin deposits in its type locality.  It has a chemical formula of KFe22+Al(Al2Si2O10)(OH)2 to KLi2Al(Si4O10)(F,OH)2.

Margarite

Considered a brittle mica, margarite, CaAl2(Al2Si2O10)(OH)2, is grayish, pale pink, or yellow, green.  Its hardness 3 ½ to 4½ on Moh's Hardness Scale.  It is found in deposits of emery (corundite) and in chlorite-mica schists.

Clintonite

Also called xanthophyllite, clintonite is another brittle mica. It is brown, golden brown, reddish brown, yellow green, or dark green in colour and has the chemical formula:  CaAlMg2(SiAl3O10)(OH)2, .  Clintonite's hardness ranges from three to six and it is found in chlorite schists.  The type locality for clintonite is in Amity, Town of Warwick, Orange Co., New York, USA. The mineral is named after a former Governor of New York State and surveyor of the Erie Canal, DeWitt Clinton

Field Notes

If you do any field geology in places with igneous and/or metamorphic rocks, you will see lots of mica as an accessory mineral.  The best way to identify which kind of mica you are seeing is by association, that is, by what other kinds of minerals are found with the mica and by what kind of rock you are looking at. 

Standard Caveat

The purpose of my weblog postings is to spark people's curiosity in geology.  Don't entirely believe me until you've done your own research and checked the evidence.  If I have sparked your curiosity in the subject of this posting, follow up with some of the links provided here.  If you want to, go out into the field and examine some rocks on your own with the help of a good field guide.  Follow the evidence and make up your own mind.

In science, the only authority is the evidence.

 








April 12, 2021

Feldspars

Figure 1 - Feldspar

Credit: Dave Dyet, 2007, Wikimedia Commons

 Feldspar is a general name for a family of minerals that have historically been grouped together because they have similar characteristics in the field.  They are commonly divided into two groups: plagioclase feldspars and alkali feldspars.  About half the minerals in the Earth's crust are feldspar of one kind or another.  Feldspars are found in most igneous and metamorphic rocks.  Among sedimentary rocks, feldspars are rare except in arkose, a sandstone where many of the grains are feldspar.  Figure 2, shows the relative abundance of the most common rock forming minerals.

Figure 2 - Mineral Abundance

General Properties

In color, feldspars are usually white, pink, gray or brown. However they can also be colorless, yellow, orange, red, black, blue, green. One variety, labradorite, has a distinctive blue colour, as shown in Figure 3.  Feldspars are usually translucent to opaque and are only rarely transparent.  If you mark a streak plate with feldspar, the streak will be white.  The specific gravity of feldspars vary from 2.5 to 2.8.  On Moh's Hardness Scale, the hardness of feldspars vary from 6.0 to 6.5.  The lustre of feldspars is usually vitreous but can be pearly on some cleavage faces.   Feldspars display perfect cleavage in two directions, usually intersecting at close to 90 degrees. This perfect 90 degree cleavage, together with consistent hardness, specific gravity and pearly luster on the cleavage faces, are the diagnostic characteristics of feldspar.

Figure 3 - Labradorite

Credit Linas Juozėnas, Wikimedia Commons

 Chemically, all feldspars are aluminum silicates with the general formula of X(Al,Si)4O8 where X is a  cation, usually calcium, potassium, sodium or a combination thereof.  Figure 4, is ternary diagram showing the varying chemistry of feldspars.

Figure 4 - Ternary Diagram of Feldspar Chemistry

As shown in Figure 4, the alkali feldspar series and the plagioclase feldspar series are two solid solution series that intersect at albite

The plagioclase series ranges from pure sodium feldspar (albite - NaAlSi3O8) to pure calcium feldspar (anorthite - CaAl2Si2O8)  Other minerals in the plagioclase series include oligioclase, andesine, labradorite, and bytownite.  Plagioclase minerals are the most common feldspar.

The alkali feldspars, also called K feldspars or K-spar, are a solid solution series that ranges from pure sodium feldspar (albite - NaAlSi3O8) to pure potassium feldspar (orthoclase and microcline -KAlSi3O8).  In between these endpoints are anorthoclase and sanidine.

In some cases, other cations substitute for the calcium, potassium and/or sodium to produce rare minerals; these include:

The Uses of Feldspar

In 2020, 23,000,000 metric tonnes of feldspar were mined worldwide. The primary uses of feldspar are for glass and ceramics.  For example, a growing segment of the market is the use of feldspar in the production of glass for solar panels. (USGS Mineral Commodity Summaries, Jan. 2021, pp 58-59)

Some feldspars are also used to make jewelry, these include Amazonite, Labradorite, Moonstone, and Sunstone.

Standard Caveat

The purpose of my weblog postings is to spark people's curiosity in geology.  Don't entirely believe me until you've done your own research and checked the evidence.  If I have sparked your curiosity in the subject of this posting, follow up with some of the links provided here.  If you want to, go out into the field and examine some rocks on your own with the help of a good field guide.  Follow the evidence and make up your own mind. 

In science, the only authority is the evidence!

 

April 5, 2021

Rock-forming Minerals - Quartz

Figure 1 - Quartz Crystals
"Quartz Crystals" by Mik Hartwell is licensed under CC BY-SA 2.0

The theme for the next few postings on this weblog will be rock-forming minerals.  There are lots of them, so this theme could carry on for a few months.  We'll look only at the most common minerals that people are likely to encounter, if you really want to dig into the subject, I suggest starting with these books:

  • Pough, F, 1998, A Field Guide to Rocks and Minerals (Peterson Field Guides), 5th Ed., Houghton Mifflin Harcourt, Boston, MA, USA

  • Deer, W., R. Howie, & J. Zussman, 1966, Introduction to the Rock Forming Minerals, Longman Group. Ltd., London, U.K.

Basic Properties of Quartz

Chemically, quartz is silicon oxide or silica.  Pure quartz is clear to white, but with impurities and inclusions it can be any of a number of colours including gray, purple, yellow, brown, black, pink, green, and red.  It is transparent to translucent and has a typically vitreous lustre.  On Mohs' Hardness Scale quartz has a hardness of seven.  When broken, quartz does not generally show cleavage but does show a characteristic conchoidal fracture.   Quartz tends to form hexagonal crystals, as is Figure 1, above.

Varieties of Quartz

The main varieties of quartz that are found in nature are:

Standard Quartz: also called low quartz or α quartz, is the most common form of quartz.  It is stable at normal temperatures and is found in most igneous and metamorphic rocks.  Sand and sandstones are mostly made up of this kind of quartz.  At high temperatures and pressures, it becomes high quartz, also called β quartz.

Chalcedony:is the microcrystalline or cryptocrystalline form of standard quartz.  The term includes a variety of stones including flint, chert, jasper, and agate as well as chalcedony.

Tridymite: is a variety of quartz often found in acid igneous rocks such as obsidian, rhyolite, andesite, trachyte, dacite and tuff.  It has slightly different optical qualities than standard quartz and often occurs as twinned crystals.

Cristobalite: like tridymite, cristobalite is also found in igneous volcanic rocks such as obsidian, rhyolite, andesite, trachyte, dacite and olivine basalt.  Opal is a hydrous cryptocrystalline form of cristobalite.

Coesite and stishovite: are high pressure/high temperature varieties of quartz formed during events such as meteor impacts.  

To get an idea of the conditions under which the various varieties of quartz form, Figure 2 is a phase diagram for silica:

Figure 2 - Silica Phase DiagramPerkins & Brady 2021


The Uses of Quartz

Among the earliest uses for quartz was to make cutting tools.  Knives, projectile points, and axes made from quartz varieties were among the earliest cutting tools that people made.  The art of flint knapping is being rediscovered by archeologists, hobbyists and people who are researching ultra-sharp surgical tools.  The conchoidal fractures of flint and other forms of chalcedony create some of the sharpest tools known to us, so if you take up flint knapping as a hobby, get some thick leather gloves.  You might also want to have some Band-Aids © and Polysporin ©.

In more modern times, flint and steel were commonly used to start fires before chemical matches were in general use.  A related use was to spark gunpowder in flintlock guns.

Another one of the original uses of quartz was as jewelry.  Semiprecious stones that are varieties of quartz include:

Other artwork made from quartz includes items such as crystal skulls and crystal balls.  A lot of this kind of artwork has been made to aid spiritual pursuits such as mediation and divination

Quartz sand is used in applications such as abrasives, masonry (as the sand in mortar), glass, ceramics, enamel ware, and for foundry sand as well as for petroleum recovery by hydraulic fracturing. 

Quartz crystals are used in electronics; some of you may have built a crystal radio at one time or another. Quartz is especially important as the source for the silicon that is used to make electronic devices like the one are using now.  Our electronic village depends on silicon derived from quartz.

Standard Caveat

I am going to include this caveat in my postings from now on.

The purpose of my weblog postings is to spark people's curiosity in geology.  Don't entirely believe me until you've done your own research and checked the evidence.  If I have sparked your curiosity in the subject of this posting, follow up with some of the links provided here.  If you want to, go out into the field and examine some rocks on your own with the help of a good field guide.  Follow the evidence and make up your own mind.

March 29, 2021

Geohazards - Tsunamis

Figure 1 - The Great Wave off Kanagawa, by Katsushika Hokusai 1

I am going to finish up my discussion of geohazards (for now) with a post on tsunamis.  Tsunamis can kill lots people and smash up their property; this is not pleasant at all.

Features of Tsunamis

The word tsunami comes from Japanese.  Living on the so called "Ring of Fire" seismic zone, the Japanese have a lot of experience with tsunamis.  An older term in English was tidal wave, but this fell out of use since its confusion with tidal bores and storm tides.

To get a tsunami, something needs to displace a vast quantity of water.  Volcanic explosions and the collapse of volcanic caldera under or next to the ocean can do this.  Earthquakes alone can cause a tsunami but they can also trigger undersea landslides that in turn lead to a tsunami.  If we really have a bad day, an extraterrestrial impactor, like an asteroid or comet, can fall into the ocean, also generating a tsunami.

The term tsunami literally translates as "harbour wave" from Japanese and this leads to an interesting feature about them.  At sea, a tsunami will appear no bigger than any other swell and may not be noticeable in a rough sea. However, once the wave approaches land, for example when it enters a harbour, the wave piles up and can become metres high.  Figure 2 illustrates this process.

Figure 2 - Tsunami approaching land 2

Infamous Tsunamis

Tsunamis can be very destructive, here is a list of some most deadly tsunamis:

Indian Ocean, December 26, 2004

Triggered by a 9.1 magnitude earthquake under the Indian Ocean, the official death toll for this tsunami was 227,898.  3

Messina, Italy, December 28, 1908

This tsunami was triggered by a magnitude 7.5 earthquake that in turn set off an undersea landslide.  Estimates of the death toll range from 100,000 to 200,000 with 70,000 of those in Messina. 3

Lisbon, Portugal, November 1, 1755

This tragedy began with an earthquake magnitude of 8.5 to 9.0 under the Atlantic Ocean offshore of Lisbon, Portugal.  The earthquake caused building collapses, fires and also triggered a tsunami with a 20 metre wave.  This unfortunate combination of events killed about 40,000 to 50,000 in Portugal, Spain, and Morocco.  3

Krakatoa, Indonesia, August 1883

The explosion of the Krakatoa volcano in August 1883 generated a tsunami 43 metres high.  About 40,000people were killed. 3

Fukushima, Japan, March 11, 2011

Also called the Tōhoku Earthquake, this began with a 9.0 magnitude earthquake under the Pacific Ocean offshore of Tōhoku on Honshu Island, Japan.  The subsequent 40 metre high tsunami killed more than 18,000 people and destroyed approximately $235 billion (USD) worth of property including critical portions of the Fukushima Dai-ichi Nuclear Generating Plant. The Dai-ichi Plant had a catastrophic failure leading to the release of dangerous levels of radiation both onto the surrounding land and into the Pacific Ocean.  3

An interesting feature of the Fukushima tsunami is that there are many stone markers in Japan showing the maximum inland intrusion of previous tsunamis.  Some of these are uphill from the Fukushima Dai-ichi Nuclear Plant. In some ways, the Fukushima Dai-ichi Plant was an accident waiting to happen since earthquakes and tsunami are as inevitable in Japan as are blizzards in Canada.  It was a lesson that did not need to be learned again.

Sauve qui peut

If you find yourself in an area where tsunami are possible, as in Figure 3, below, such as along the sea shore, keep the following in mind:

  • If you feel a earthquake, prepare to seek higher ground.

  • Listen on the radio for tsunami warnings, some places also send out warnings to smart phones and some places have no warning system at all

  • If you see the ocean suddenly recede, this means that the tsunami is imminent. Go to higher ground immediately.  Don't stick around to get photos and videos.  Getting that selfie might kill you.

Figure 3 - Tsunami Risk Map 4

References

  1. Wikimedia Commons, Mar.2015, File:Tsunami by hokusai 19th century.jpghttps://commons.wikimedia.org/wiki/File:Tsunami_by_hokusai_19th_century.jpg

  2. WPClipart, accessed March 2021, tsunami approaching landhttps://wpclipart.com/weather/tsunami/tsunami_approaching_land.png.html

  3. Johnson, B., Aug. 2020, World's Worst Tsunamis, ThoughtCo, thoughtco.com/worlds-worst-tsunamis-3555041. 

  4. Disaster Rally, accessed March 2021,What to Do in Case of Tsunami Before, During, and After, https://disasterrally.com/what-to-do-in-case-of-tsunami/

March 22, 2021

Geohazards - Landslides

Figure 1 - Last Chance Grade Landslide 1

Stevie Nicks wrote her song, Landslide, in response to the many professional troubles that she and her band, Fleetwood Mac, were having at the time.  Everything seemed to be crashing down at once, just like a landslide 2.   It's a beautiful song about coping with change and loss and is a good place to start a discussion on landslides.

Landslide Causes

The basic cause of landslides is the action of gravity on a vulnerable geological feature combined with something that triggers the failure.  More specifically, landslides may be caused by one or more of the following factors:

1.       Geological causes
  • Weak or sensitive materials

  • Weathered materials

  • Sheared, jointed, or fissured materials

  • Adversely oriented discontinuity (bedding, schistosity, fault, unconformity, contact, and so forth)

  • Contrast in permeability and/or stiffness of materials

 2.       Morphological causes
  • Tectonic or volcanic uplift

  • Glacial rebound

  • Fluvial, wave, or glacial erosion of slope toe or lateral margins

  • Subterranean erosion (solution, piping)

  • Deposition loading slope or its crest

  • Vegetation removal (by fire, drought)

  • Thawing

  • Freeze-and-thaw weathering

  • Shrink-and-swell weathering

3.       Human causes
  • Excavation of slope or its toe

  • Loading of slope or its crest

  • Draw down of reservoirs

  • Deforestation

  • Irrigation

  • Mining

  • Artificial vibration

  • Water leakage from utilities

(From USGS, 2004 3)

Features of a Landslide

Before discussing the types of landslides, it is helpful to identify the features of a landslide, as shown in Figure 2, below.

Figure 2 -Features of a Landslide 3

Types of Landslides

Figure 3, below, illustrates the main types of landslides.

Figure 3 - Types of Landslides 3

In a rotational landslide (Fig. 3A), the surface of rupture is curved concavely upward and movement of the slide is roughly rotational about an axis that is parallel to the ground surface and transverse across the slide 3.

Translational landslides (Fig. 3B) are where the landslide mass moves along a roughly planar surface with little rotation or backward tilting 3.

A block slide (Fig 3C) is a kind of translational slide where the moving mass consists of a single unit or a few closely related units that move downslope as a relatively coherent mass 3.

A rock fall  (Fig. 3D is just as the name suggests; masses of geologic materials, such as rocks and boulders become detached from steep slopes or cliffs 3.

In a topple, (Fig. 3E)  the failure of the material unit is by the forward rotation of a unit or units about some pivotal point, below or low in the unit 3.

Debris flows (Fig. 3F) are a form of rapid mass movement in which a combination of loose soil, rock, organic matter, air, and water mobilize as a slurry that flows downslope 3.  I discussed an example of  this in the March 8 posting on debris flows from volcanic activity. 

A debris avalanche (Fig.3G) is an extremely fast variety of a debris flow 3.  A volcanic lahar is a good example.

Earthflows (Fig. 3H) have a characteristic “hourglass” shape; the slope material liquefies, runs out, and forms a bowl or depression at the head of the earthflow 3. Liquefaction of silt and sand deposits commonly happens during earthquakes.

In this context, creep (Fig. 3I) isn't the obnoxious fellow leering at passersby but, rather, is the slow, sometimes almost imperceptible, steady, downward movement of soil and/or rock 3.

Lateral spreads (Figure 3J) occur on very gentle slopes or flat terrain and are marked by lateral movement of the soil, often due to liquefaction of saturated soils with little cohesion. Lateral spreads are often triggered by earthquakes but can also be artificially induced 3.

Worldwide Risks of Landslides

Landslides are most common in areas of high relief, such as in mountainous terrain.  Risks to human life increase where there are greater densities of population; both from the number of people in proximity to the potential unstable ground and from the likelihood of human activity that increases the instability. Areas of high rainfall are also prone to landslides where those areas coincide with the terrain and human factors.  

Figure 4, prepared by the NASA Earth Observatory, shows the worldwide risks of landslides to human life and property.

Figure 4 - Global View of Landslide Susceptibility 4

Afterword

As a geohazard, landslides are a serious threat to human life and property.  Understanding the causes and mechanics of landslides is a necessary precaution in areas prone to them.  Just  as important is understanding how human activities can increase or mitigate the threat from landslides.

Back to where we started at the beginning of the post. We saw Stevie Nicks writing Landslide when her professional life seemed to be falling down. So, what happened next?  Well, Landslide went on to be a big hit.  Since then Stevie Nicks has had a successful career, both with Fleetwood Mac and also as a solo artist.  Other singers have covered the song and Stevie Nicks continues to sing it to this day.  While having little to say on the science of landslides, art like the song Landslide can teach us lessons about coping with the inevitable grief and loss that will occur in our lives.

Where there's life, there's hope.

References

  1. Wikimedia Commons, Feb. 2021, File:2020-0301 LastChanceGradeLandslide.jpg, https://commons.wikimedia.org/wiki/File:2020-0301_LastChanceGradeLandslide.jpg

  2. Wikipedia, Mar. 2021, Landslide (Fleetwood Mac song), https://en.wikipedia.org/wiki/Landslide_(Fleetwood_Mac_song)

  3. United States Geological Survey (USGS), Jul. 2004, Landslide Types and Processes, https://pubs.usgs.gov/fs/2004/3072/fs-2004-3072.html 

  4. NASA Earth Observatory, March, 2017, A Global View of Landslide Susceptibility,   https://earthobservatory.nasa.gov/images/89937/a-global-view-of-landslide-susceptibility?src=ve

March 15, 2021

The latest edition of the Engineers Geoscientists Manitoba newsletter, The Keystone Professional is online at http://www.enggeomb.ca/pdf/Keystone/21Spring.pdf.  My article under Geology and Society is on page 16

March 15, 2021

Earthquakes in Divers Places

Figure 1 - Croatian Earthquake, December 2020 1

For nation shall rise against nation, and kingdom against kingdom: and there shall be earthquakes in divers places, and there shall be famines and troubles: these are the beginnings of sorrows. 2

When Jesus of Nazareth warned his followers of what to expect in the future, he included earthquakes among the many troubles that were coming their way.  This isn't surprising, since in Jesus' day, and indeed for most of  human history, earthquakes and other natural disasters were seen as divine punishment or warning that something important was coming our way.  However, with the development of the modern science of geology, we have a better understanding of earthquakes as natural processes.  

Faults

So, what is an earthquake? An earthquake is a movement of a portion of the earth's crust, usually along a pre-existing break in the crust that we call a fault. The animations below show the three main kinds of faults.

Strike-slip faults,also called transform faults  are vertical (or nearly vertical) fractures where the blocks have mostly moved horizontally. If the block opposite an observer looking across the fault moves to the right, the slip style is termed right-lateral; if the block moves to the left, the motion is termed left-lateral.  Animation link  3

Normal, or Dip-slip, faults are inclined fractures where the blocks have mostly shifted vertically. If the rock mass above an inclined fault moves down, the fault is termed normal, whereas if the rock above the fault moves up, the fault is termed a Reverse fault.Animation link  4

A thrust fault is a reverse fault with a dip of 45° or less, a very low angle. The animation shows a reverse fault which is a steeper-angle fault, but it moves the same way. Animation link  5

Causes of Earthquakes

So what can cause the earth's crust to move?  There are four main causes:

  1. Movement of tectonic plates

  2. Volcanism

  3. Isostatic rebound

  4. Anthropogenic causes

Tectonic Plate Movement

The earth's crust is divided into a number of distinct plates.  Plate tectonics is worth at least one blog post, maybe more, and I shall discuss it in future postings.  For now,  it is enough to note that the plates move.  Earthquakes caused by tectonic activity occur where tectonic plates move next each other.

Figure 2 shows the major tectonic plates in the world and the direction of movement.

Figure 2 - Tectonic Plates 6

Volcanism

The movement of magma and lava before and during volcanic eruptions can cause many earthquakes.  As I discussed last week, current earthquakes at the Reykjanes Peninsula in SW Iceland portend volcanic eruptions there 7.

Isostatic Rebound

When the continental glaciers began melting around 15,000 years ago, a great weight was taken off the earth.  Once that weight was removed, the earth's crust rebounded.  It isn't a gradual process but occurs as intermittent movements.  These movements cause earthquakes, generally minor.  Many of the earthquakes in Canada, especially those occurring east of the Rockies,  are due to glacial rebound.

There is a good summary of  isostatic rebound on the Wikipedia page Post-glacial rebound 8.

Anthropogenic Causes

Human activities can cause earthquakes, these activities include

  • Mining:  collapsing mine tunnels in underground coal mining

  • Mining and construction: excavation with explosives

  • Oil and natural gas extraction: formation fracturing (fracking)

  • Waste Disposal: injecting waste fluids underground

  • Dams: the weight of water behind a dam

  • Weapons: nuclear weapons testing

One concern is that human activity can trigger existing faults and inadvertently cause large earthquakes 9.   This can happen with the activities listed above.

Infamous Earthquakes

When earthquakes occur in densely populated areas, huge numbers of people can be killed, either by collapsing buildings or by knock on effects such as tsunami.  Here is a list of the 10 deadliest earthquakes in history 10:

1.       Shaanxi, China (1556)

With an estimated strength of 8.0 on the Richter Scale,  this earthquake killed approximately 830,000 people on the morning of  23rd January, 1556.  Many people the Shaanxi region lived in caves dug in the loess soil and the earthquake collapsed many of these caves.  Also, the earthquake triggered landslides, killing more people. 

2.       Haiyuan, China (1920)

In the evening of December 16th, 1920, an earthquake measuring 7.5 to 8.5 on the Richter Scale struck Gansu Province in China.  Estimates of the total death toll attributed to the earthquake range between 240,000 and 275,00 and include people who perished from exposure in the harsh winter weather following the earthquake.

3.        Tangshan, China (1976)

 Often called The Great Tangshan Earthquake, this earthquake struck the city of Tangshan, China on July 28th, 1976 at 4:00 AM.  Measuring 7.8 on the Richter Scale, the initial earthquake was followed by an aftershock 16 hours later.  Of the approximately 1 million inhabitants of Tangshan, approximately 255,000 people were killed, mostly by collapsing buildings.

4.       Antioch, Eastern Roman Empire (526)

Located at modern day Antakya in Turkey, ancient Antioch was a major city in the Eastern Roman Empire.  The initial 7.0 magnitude earthquake in 526 was followed by aftershocks that lasted for 18 months.  Approximately 250,000 people were killed, mostly by falling buildings.

5.       Indian Ocean (2004)

On Boxing Day 2004, a 9.3 magnitude earthquake lasting almost 10 minutes occurred under the Indian Ocean triggering a massive tsunami.  Approximately 230,000 people were killed in Indonesia, Sri Lanka, India and Thailand. 

6.       Aleppo, Syria (1138)

Located at the north end of the Dead Sea rift system, Aleppo, Syria is prone to periodic earthquakes.  Several earthquakes hit the region from October 1138 to May 1159 leading to the deaths of approximately 230,000, mostly from collapsing buildings.

 7.       Haiti (2010)

The main 7.0 magnitude earthquake occurred January 12, 2010 and was followed by 52 aftershocks, some with a magnitude of 4.5 .  The estimated death toll was more than 160,000.

 8.       Damghan, Persia (856)

Occurring at Damghan in modern day Iran, the 856 earthquake had an estimated magnitude of 7.9.  The earthquake affected an area with a 350 km radius around the epicentre.  Approximately 200,000 people were killed in the towns of Ahevanu, Asta, Tash, Bastam and Shahrud as well as in surrounding villages.

 9.       Dvin, Armenia (893)

Dvin, the capital of ancient Armenia, (now ruins near Verin Dvin, Armenia) was hit by an earthquake on December 26, 893.  Approximately 150,000 people were killed.

 10.   Messina, Italy (1908)

Hitting the city of Messina with an estimated magnitude of 7.1,  the December 28, 1908 earthquake destroyed up to 90% of the buildings in the city and generated a 12 m high tsunami.  About 123,000 people died as the result of the building collapses and tsunami.

As always, feel free to follow up on the references listed below to learn more about earthquakes.

References 

  1. USA Today, Dec. 29, 2020, Rescuers comb through rubble after Croatia earthquake, https://www.usatoday.com/videos/news/world/2020/12/29/rescuers-comb-through-rubble-after-croatia-earthquake/4079848001/

  2. Gospel of Mark, Ch. 13, v. 8, King James Version, https://biblehub.com/kjv/mark/13.htm 

  3. United States Geological Survey (USGS), 2014, Strike-Slip Fault, https://www.usgs.gov/media/videos/strike-slip-fault

  4. USGS, 2014, Normal Fault, https://www.usgs.gov/media/videos/normal-fault

  5. USGS, 2014, Thrust Fault, https://www.usgs.gov/media/videos/thrust-fault

  6. Weebly, Accessed March 2021, Plate Tectonics, Plate Boundaries & Tectonics, https://plateboundaries111.weebly.com/plate-tectonics.html

  7. McGarvie, D., Mar. 4, 2021, South-west Iceland is shaking – and may be about to erupt, The Conversation, Academic Journalism Society, https://theconversation.com/south-west-iceland-is-shaking-and-may-be-about-to-erupt-156510

  8. Wikipedia, January 2021, Post-glacial rebound, https://en.wikipedia.org/wiki/Post-glacial_rebound

  9. Mulargia, F., Bizzarri, A., 2014, Anthropogenic Triggering of Large EarthquakesSci Rep 4, 6100. https://doi.org/10.1038/srep06100

  10. TOP10HQ, Top 10 Deadliest Earthquakes in History, https://www.top10hq.com/top-10-deadliest-earthquakes-history/, accessed March 2021





March 8, 2021

More on Volcanoes as a Geohazard

Figure 1 - Mt. Sinabung, March 2, 2021  1

After last week's posting, two more volcanoes were in the news:  Mt. Sinabung in Indonesia erupted 1 and geologists warned that Keilir Volcano in Iceland will soon erupt 2.  With that in mind, I thought that it would be worthwhile to look further into the dangers from volcanoes.

The Nature of Lava

Erupting volcanoes spew out hot gases, molten rock, rock fragments and dust, so there are some pretty obvious dangers.  Just how dangerous depends on the nature of the lava produced by the eruption.  Lava varies in viscosity from fairly fluid to very viscous.  Fluid lava will simply flow out of the volcano's pipe while viscous lava may explode.  The presence or absence of water will also affect the eruption.

The viscosity of lava depends in large part its chemical composition, especially its silica content.  The best way to describe this composition is by way of the minerals that will crystallize out of the melt.  Figure 2 shows a general classification of igneous rocks, volcanic rocks are considered extrusive igneous rocks.

Figure 2 - General Classification Igneous Rocks 3

In general, the most fluid lavas will be those that form mafic and ultramafic rocks. The term "mafic" refers to the dark colour of rock dominated by minerals such as olivine, pyroxene and calcium rich plagioclase feldspar.  At the other end of the spectrum, lavas that produce felsic rock will tend to very viscous;  the term "felsic" refers to the lighter colour of the rock dominated by minerals such as orthoclase (potassium feldspar), quartz, and sodium rich plagioclase. 

Hazards from Volcanic Eruptions

Lava flows

Figure 3 - Eruption of Kilauea  4

Molten rock flowing directly from a volcanic pipe or vent is probably the safest kind of volcanic eruption to be around.  An example of a lava flow are the ongoing eruptions at Kilauea, Hawaii.

Although relatively fluid, molten lava moves slowly and is easily avoided.  However, there are distinct dangers from flowing lava. Hot flowing lava will cause any flammable item in the vicinity to catch on fire including  vegetation and wooden structures.  Also, flowing lava can bury anything that gets in the way its way including cars, roads and buildings.  5

Pyroclastic Flows

Figure 4 - Pyroclastic Flow,Mt. Merapi, Indonesia. 6

Moving downhill at 80 km/hr; you really want avoid these hellishly hot (200 - 700 degrees C ) avalanches of volcanic dust, gases and steam. Be prepared to run far, pyroclastic flows can travel five to fifteen km from the volcanic eruption.  Pyroclastic flows are associated with explosive eruptions such as at Mt. Pinatubo, Philippines, El Chicon, Mexico and Mt. Merapi, Indonesia (Fig. 4, above). 5

Debris Flows and Lahar

Figure 5 - Lahar at Mt. St. Helens 7

Another hazard from volcanic are debris flows, sometimes called lahars.  Mixtures of volcanic ash, soil, rocks, water, and any other debris the lahar pick up along the way (trees, dead bodies), lahars travel down the steep slopes of volcanoes, during or after volcanic eruptions. The water often comes from melted ice.  The debris flow has the consistency of cement, and will often travel long distances along river valleys downstream from the volcano.  Lahars from Mt. St. Helens, in Washington State,  traveled up to 97 km from the volcano.  5

Landslides

Volcanic landslides occur when the structure of the main body of a volcano fails before, during or after an eruption 5.   There was a landslide immediately before the main eruption of Mt. St. Helens.  See this video from the USGS; the landslide is discussed beginning at 4:08.

I'll discuss more about landslides in an upcoming posting.

Volcanic Ash and Tephra

Explosively erupting volcanoes discharge various sizes of material ranging from very fine silt to cobbles and boulders  The fine grained material is usually called "volcanic ash" and the larger material is often called "tephra" 5.  Tephra cobbles and boulders are sometimes called "volcanic bombs".

The obvious hazard from volcanic ash and tephra is burial. So, unless you want to become a future exhibit in a museum, like the unfortunate inhabitant of Pompeii below, you would be wise to vacate areas suffering volcanic ash falls.

Figure 6 - Cast of Pompeii Resident8

You may have to travel far, though; volcanic ash can travel hundreds of miles from the volcanic eruption 5.

Another danger from volcanic ash is inhalation. Volcanic ash is made up of fine particles of volcanic glass 5; inhaling volcanic glass can lead to respiratory failure.  Volcanic ash, carried aloft, high into  the atmosphere, can also cause damage to jet engines. It can be a major hazard for airline travel, such as when the Eyjafjallajokull Volcano in Iceland erupted in 2010 9.  

Eyjafjallajokull is on the Reykjanes Peninsula in SW Iceland. Also on the Reykjanes Peninsula is  the Keilir Volcano, which as we noted at the beginning of this post,  may be ready to erupt 2.  Due to the earthquakes and likely volcanic activity, the Iceland civil defense authorities are warning people of the dangers of landslides and rock falls 10.  Icelanders, known to be fairly common sense about these things, refer to the volcanic activity on Reykjanes Peninsula as “tourist eruptions” 10, i.e. good for the tourist business.

Volcanic Gases

Volcanic eruptions usually include emissions of various gases such as steam, carbon dioxide, sulphur dioxide and hydrogen sulphide.  Sometimes the gaseous emissions alone are sufficient to cause great harm.  Sulphur dioxide and hydrogen sulphide are both poisonous gases and high concentrations of carbon dioxide present an asphyxiation hazard.   5

The release of carbon dioxide from Lake Nyos, a lake in a volcanic crater in Cameroon, killed approximately 1700 people August 26, 1986 11.

Pay Your Money and Take Your Chances

Volcanoes are both dangerous and beautiful.  If you live in the vicinity of an active volcano, familiarize yourself with its eruption history and characteristics.   If you plan to visit an active volcano, enjoy the spectacle but keep the risks in mind.  Try not to be like these tourists at Eyjafjallajokull.

Notes on Grain Size

When referring to the grain size of material, I use the Wentworth Scale 12, as shown in Table 1, below.

Table 1 - Wentworth Grain Size Scale 13

References

  1. Howes, N, March 2, 2021, Indonesian volcano erupts again, here's why it has frequent  blasts, Yahoo News, https://news.yahoo.com/indonesian-volcano-erupts-again-heres-014300551.html?guccounter=1&guce_referrer=aHR0cHM6Ly9kdWNrZHVja2dvLmNvbS8&guce_referrer_sig=AQAAAFGdwz75_gFUlVLxURwBVLYf0GyndgPsVIe49WPEnKdqgYjy17FyPOqIfDWfzSdrbarYHjblsT7EWI6HJfpt0goEgFZ316LWnYUgLbGCxJKGgAFKigY6YFhXTFJ2A9trMDVc8XfT3M7U2w06-SM7SkfwvgJfO4CLeWSw0EBiuoeT

  2. Henley, J., March 3, 2021, Scientists in Iceland say ‘strong signs’ volcanic eruption is imminent, The Guardian, https://www.theguardian.com/world/2021/mar/03/scientists-in-iceland-say-strong-signs-volcanic-eruption-is-imminent

  3. Wikimedia Commons, Oct.2020, File:Igneous rocks.jpg, https://commons.wikimedia.org/wiki/File:Igneous_rocks.jpg

  4. Wikimedia Commons, Sept.2020, File:Eruption of the Kilauea volcano.jpg, https://commons.wikimedia.org/wiki/File:Eruption_of_the_Kilauea_volcano.jpg

  5. American Geosciences Institute, 2021, What kinds of hazards are associated with volcanic eruptions?, https://www.americangeosciences.org/critical-issues/faq/what-kinds-hazards-are-associated-volcanic-eruptions

  6. Mongin, M., Jan. 2009, Pyroclastic Flow, Penn State, "pyroclastic flow" by pennstatenews is licensed under CC BY-NC 2.0, https://www.flickr.com/photos/53130103@N05/4950560761

  7. Wikimedia Commons, Oct.2020, File:Lahar, Mount St. Helens.jpg, https://commons.wikimedia.org/wiki/File:Lahar,_Mount_St._Helens.jpg

  8. Wikimedia Commons, Sept.2020, File:Pompeii casts 06.jpg, https://commons.wikimedia.org/wiki/File:Pompeii_casts_06.jpg

  9. USGS Volcanic Ash Falls Impacts Group, Feb. 2016, Volcanic Ash Impacts and Mitigation, Aviation, https://volcanoes.usgs.gov/volcanic_ash/ash_clouds_air_routes_eyjafjallajokull.html

  10. McGarvie, D., Mar. 4, 2021, South-west Iceland is shaking – and may be about to erupt, The Conversation, Academic Journalism Society, https://theconversation.com/south-west-iceland-is-shaking-and-may-be-about-to-erupt-156510

  11. Oregon State University, 2021, Volcano World, Lake Nyos - Silent but Deadly, http://volcano.oregonstate.edu/silent-deadly

  12. Wentworth, C.K., 1922, A Scale of Grade and Class Terms for Clastic Sediments, The Journal of Geology, Vol. 30, No. 5 (Jul. - Aug., 1922), pp. 377-392, The University of Chicago Press, https://www.jstor.org/stable/30063207?seq=1#metadata_info_tab_contents

  13. Wikimedia Commons, September 2020, File:Wentworth scale.png, https://commons.wikimedia.org/wiki/File:Wentworth_scale.png

March 1, 2021

Geohazards - Volcanoes

Figure 1 - Mount Etna Volcano Feb. 24, 2021. 
(Credit: AP Photo/Salvatore Allegra)1

I noticed in the news this past week that Mount Etna in Italy is erupting again 2, so I thought that the subject of geohazards, and volcanoes in particular, would make a good subject for this week's posting.  I'll continue with the theme of geohazards for the rest of March 2021.

What's a Geohazard?

Geology is about the real world, and the world can be a dangerous place.  Geohazards are any dangerous geological condition. These include: volcanoes, earthquakes, landslides, tsunami and floods.   There are many ways that the Earth can kill us and we had better be aware of those threats for our own self protection.

For general information on geohazards, you might want to read the Natural Resources Canada document, Evaluation of the Geohazards and Public Safety Program Sub-activity 3.  The Canadian Geotechnical  Society has periodic conferences on geohazards and has published the proceedings of those conferences 4.  There is also an international journal, GeoHazards on the subject 5.

Where are Volcanoes Found?

Volcanoes on the Earth are intimately connected to the movement of the crustal plates in the process called Plate Tectonics. (I'll have to discuss Plate Tectonics in a future blog posting.)   Generally, volcanoes are found at plate boundaries.  Volcanoes can also be found at so called "hot spots" in the middle of a plate.

Figure 2 shows the general location of the tectonic plates and the locations of volcanoes.

Figure 2 - Volcanoes and Plate Boundaries 6

Active volcanic regions in Canada are found in five areas in the Western Cordillera. Figure 3 shows the locations of active volcanoes in Canada.

Figure 3 - Active Volcanoes in Canada 7

Anatomy of a Volcano

The main features of a volcano are, from the bottom up:

  •  The magma chamber, this is where the molten magma accumulates;

  • The pipe through which the magma flows to emerge through the vent in the chamber as either lava, volcanic ash and/or volcanic bombs;

  • The cone that is made up of accumulated layers of lava, volcanic ash and/or volcanic bombs.

Figure 4 - Anatomy of a Volcano

 Types of Volcanoes

Generally, there are four kinds of volcanoes, the kind of lava produced by a volcano will largely determine the form that a volcano takes:

1. Cinder cone volcanoes 

These are made up of a collection of volcanic dust, pebbles, cobbles and boulders (volcanic bombs).  Volcanoes that erupt viscous lavas will form cinder cones. Paricutin, in Mexico, is a typical cinder cone volcano.  8

Figure 5 - Paricutin Volcano  9

2. Shield volcanoes 

These are made up of consecutive lava flows formed from relatively fluid lava as in Figure 6, below.  The islands of Hawaii and Iceland are giant shield volcanoes. 8

Figure 6 - Internal Structure of a Shield Volcano  8

3. Composite volcanoes

These are made up of different layers of lava flows and volcanic ash.  These are formed where the underlying magma chamber produces alternating fluid lava and viscous lava as in Figure 7, below. 8

Figure 7 - Internal Structure of a Composite Volcano   8

4. Lava domes

These form from relatively small, bulbous masses of lava, too viscous to flow any great distance.  As a result, when extruded through the pipe, the lava piles over and around the volcano's vent.  The Novarupta Dome, formed during the 1912 eruption of Katmai Volcano in Alaska, is an example of a lava dome. 8

Figure 8-Novarupta Dome, Mt. Katmai, Alaska10

Some Examples of Famous Volcanic Eruptions

Volcanoes can be deadly.  Here are a four examples from history:

Thera, Greece, 1628 B.C

The volcano on the island of Thera (also called Santorini) blew up with a huge explosion around 1628 B.C.  Approximately 40,000 people were killed by the explosion and the subsequent 40 foot tsunamis.  The blast was heard 3,000 miles away 11.

The destruction of the island severely weakened the Minoan Civilization and, according to authors such as Dr. Charles Pellegrino, may be the source of Plato’s myth about Atlantis  12.

Mt. Vesuvius, 79 AD

The eruption of Mt. Vesuvius in 79 AD was famously recorded by Gaius Plinius Caecilius Secundus(Pliny the Younger) in his correspondence with the historian Publius Cornelius Tacitus (Tacitus).  In Letters LXV and LXVI, Pliny the Younger describes the eruption of Vesuvius and the death of his uncle, Gaius Plinius Secundus (Pliny the Elder)13

In those days, the Romans believed that leading citizens should risk their lives for the common good.  Pliny the Elder, a Roman Senator, died trying to rescue people from the eruption. He was among the approximately 1,500 people that perished as a result of the eruption of Mt. Vesuvius 14.

The eruption of Mt. Vesuvius in 79 AD buried the cities of Pompeii and Herculaneum and archaeological studies of the two buried cities have given us a unique glimpse into life during Roman times.

Tambora 1815

Tambora is found in Indonesia and on April 10, 1815 it erupted with what has been described as the greatest explosion in recorded history.  The eruption spewed an estimated 36 cubic miles of volcanic ash into the atmosphere.  Approximately 88,000 people were killed in the explosion.  15

 The following year was called the “Year Without Summer” and was marked by crop failures, famine and general gloominess. Mary Shelley wrote her famous novel Frankenstein, that summer.  16

Krakatoa, August 1883

Krakatoa lies in the Sunda Straight between Java and Sumatra. In May 1883, it began to erupt.  On August 27, 1883, it exploded with an equivalent force of 200 megatons of TNT.  The explosion and subsequent tsunami killed approximately 36,000 people.  17

Mitigating the Hazard

Volcanoes are notoriously dangerous.  If a volcano goes off in your neighbourhood, the best course of action is to GET THE HELL OUT OF THERE and observe the volcano from a safe distance. 

Volcanologists, geologists who study volcanoes, are brave people as in Figure 9, below.  I think that it would be fun to do this, don't you?

Figure 9 - USGS Geologist Sampling at Mauna Loa Volcano, Hawaii  18

Besides physical distancing when an eruption occurs, the best long term mitigation strategy for the danger from volcanoes is to study them.  As a society, supporting the work of volcanologists is a good investment.  We still have a lot to learn about volcanoes, especially about predicting the timing and scale of eruptions.   Failure to prepare ourselves for the dangers in this world could be fatal for millions of people.

If you have a taste for disaster movies involving volcanoes, this is a good film.

As always, this is a big subject, and if volcanoes interest you, follow up on the references listed below.

References

  1. Associated Press, Feb. 25, 2021, Mount Etna's recent eruption is a spectacular volcanic show, https://www.foxnews.com/world/mount-etna-puts-on-its-latest-spectacular-show

  2. Volcano Discovery, Feb. 2021, Etna volcano updates and eruption news, https://www.volcanodiscovery.com/etna/news.html

  3. Natural Resources Canada, 2013, Evaluation of the Geohazards and Public Safety Program Sub-activity (PAA Sub-activity 3.1.5), https://www.nrcan.gc.ca/nrcan/plans-performance-reports/strategic-evaluation-division/reports-plans-year/evaluation-reports-2014/evaluation-geohazards-and-public-safety-program-sub-activity-paa-sub-activity-315/16274

  4. The Canadian Geotechnical Society, 2019, Geohazards, CGS Geohazards Conference Proceedings, https://www.cgs.ca/geohazards_committee.php

  5. GeoHazards (ISSN 2624-795X), https://www.mdpi.com/journal/geohazards

  6. Wikimedia Commons, Feb. 2017, File:Map plate tectonics world.gifhttps://commons.wikimedia.org/wiki/File:Map_plate_tectonics_world.gif

  7. Gravesande, D, July 2018, Volcanoes in Canada: Are they ready to rumble?, Natural Resources Canada, https://www.nrcan.gc.ca/simply-science/21282

  8. Watson, J., 2011, Principal Types of Volcanoes, United States Geological Survey, https://pubs.usgs.gov/gip/volc/types.html

  9. Wikimedia Commons, November 2020, File:Paricutín volcano.jpg, https://commons.wikimedia.org/wiki/File:Paricut%C3%ADn_volcano.jpg

  10. Wikimedia Commons, April 2019, File:Alaska Katmai Novarupta-Dom.jpg, https://commons.wikimedia.org/wiki/File:Alaska_Katmai_Novarupta-Dom.jpg

  11. Whipps, H., 2008, How The Eruption of Thera Changed the World, https://www.livescience.com/4846-eruption-thera-changed-world.html

  12. Pellegrino, C. R., 1991, Unearthing Atlantis, Random House Inc., New York, N.Y., U.S.A.

  13. Bosanquet, F. C. T. (ed.), 2001, Letters LXV and LXVI in Letters of Pliny By Gaius Plinius Caecilius Secundus, translated by Translated by William Melmoth, https://www.gutenberg.org/files/2811/2811-h/2811-h.htm#link2H_4_0065

  14. Wikipedia, February 2021, Eruption of Mount Vesuvius in 79, https://en.wikipedia.org/wiki/Eruption_of_Mount_Vesuvius_in_79

  15. Live Science, 2012, The Greatest Eruption in Human History: Mount Tambora, https://www.livescience.com/31337-mount-tambora-image.html

  16. National Center for Atmospheric Research, UCAR, 2012, Mount Tambora and the Year Without a Summer, https://scied.ucar.edu/shortcontent/mount-tambora-and-year-without-summer

  17. Mary Bagley, M., 2017, Krakatoa Volcano: Facts About 1883 Eruption, https://www.livescience.com/28186-krakatoa.html

  18. Wikimedia Commons, June 2009, File:Sampling lava with hammer and bucket.jpg, https://commons.wikimedia.org/wiki/File:Sampling_lava_with_hammer_and_bucket.jpg












February 22, 2021

Hydrogen, Helium, Lithium

Introduction

In last week's post on where the elements originated I noted that Hydrogen, Helium and Lithium were the only three elements created in the Big Bang.  So, what is the geology of these three elements?

 Hydrogen

Although it is the most common element in the Universe,  free hydrogen is not common on the Earth. this is because free hydrogen is very reactive and the use of hydrogen can come to explosive ends as in Figure 1.

Figure 1 - Hydrogen is Very Reactive 
https://commons.wikimedia.org/wiki/File:Hindenburg_disaster.jpg

Most of the hydrogen on earth is found in water, which is made up of hydrogen and oxygen.  Hydrogen  is also found in hydrocarbons: petroleum, natural gas and coal.

I won't spend too much time on hydrogen geology in this week's post since it can include a lot of topics, each of which is worth a post, or series of post, of its own:

Water
  • Erosion and sedimentary deposition;

  • Ocean and coastal geology,;

  • Caves and karst topography;

  • Glacial geology and periglacial landforms;

  • Hydrogeology and groundwater;

  • Minerals containing water such as hydrates.

 Hydrocarbons
  • Exploration and extraction of petroleum, natural gas and coal deposits;

  • The origin of petroleum, natural gas and coal;

  • The economics of hydrocarbons including depletion.

 The Hydrogen Economy
  • Hydrogen as an alternative energy source

 I'll explore these themes in future posts.

Helium

Although helium is the second most abundant element in the Universe, it is rare on Earth.  As a noble gas , it does not combine with other elements and, as a light gas, little would have remained in the atmosphere after the initial formation of the Earth.  Most helium found in the Earth today is found as a component of natural gas, having been formed as a result of the radioactive decay of Uranium 238, as in Figure 2.

Figure 2 - Helium from Radioactive Decay of U 238From : Weebly.com, Radioactive Decay,
https://radioactivedecay9.weebly.com/what-is-radioactive-decay.html

According the U.S. Geological Survey, helium is used for the following applications:

  • magnetic resonance imaging, 30%;

  • lifting gas, 17%;

  • analytical and laboratory applications, 14%;

  • welding, 9%;

  • engineering and scientific applications, 6%;

  • leak detection and semiconductor manufacturing, 5% each;

  • and various other minor applications, 14%.          1

 The United States has the largest reserves of Helium, estimated at 3,100 million cubic metres (MCM), followed by Algeria (1,800  MCM) and Poland (25 MCM) 1.

In Canada, most helium is produced in Saskatchewan and Alberta as a by-product of natural gas production.  Construction of a new helium purification facility was announced in May 2020 2 for completion in July 2021 3.  This is expected to be Canada's largest helium purification plant 2, 3.

Lithium

The last of our three Big Bang elements is lithium. Most people are familiar with lithium as a component in lithium ion and lithium polymer batteries.  The main uses of lithium are:

  • batteries, 65%;

  • ceramics and glass, 18%;

  • lubricating greases, 5%;

  • polymer production, 3%;

  • continuous casting mold flux powders, 3%;

  • air treatment, 1%; and

  • other uses, 5%.                 4

 Lithium is also a highly reactive metal and its use in lithium ion or lithium polymer batteries is known to cause fire in certain circumstances. Here is an example of what can happen 5; as the man says DON'T DO THIS AT HOME!

About ten minerals are known to contain lithium; in igneous rocks the most common lithium minerals are spodumene, petalite and lepidolite 6.  In sedimentary rocks, lithium is found in the clay mineral, hectorite. Lithium can also be extracted from brines 6.  The environments that lithium minerals and dissolved lithium are found include:

  • Lithium-Cesium-Tantalum Pegmatite Deposits;

  • Lithium-Enriched Granites;

  • Lithium Brine Deposits in Closed Basins;

  • Lithium in Other Brines;

  • Lithium-Clay Deposits;

  • Lithium-Zeolite Deposits.             6

 Figure 3 shows the location of Lithium-Cesium-Tantalum Pegmatite Deposits worldwide.

Figure 3 Worldwide Lithium-Cesium-Tantalum Pegmatite Deposits

Figure 4 shows the location of lithium enriched brine and clay deposits worldwide

Figure 4  Worldwide Lithium Enriched Brine and Clay Deposits 6

If electric vehicles (EV) become more popular, we can expect a greater demand for lithium to make the batteries for the EV.  One estimate of future demand was published in Mining.com Jan. 27, 2021 indicating that if Tesla goes forward with their plan to build 20 million cars per year, it will require 127,302 tons of lithium per year 7.

Many people believe that EV are more environmentally friendly than internal combustion engine (ICE) vehicles.  After all, EV make no emissions.  However, the environmental cost of any vehicle system has to include not only the emissions of the individual vehicles, but also the environmental effects of building the vehicles.  In the case of the lithium required for batteries, we should consider the environmental effects of lithium mining or brine extraction that can lead to surface and groundwater pollution as well as landscape destruction 8.    

As always, environmental costs are a matter of trade offs.  Switching to EV will reduce air pollution, especially in large cities where there are many motor vehicles. However, the trade off will be moving the environmental impacts from prosperous urban environments to the places where the necessary minerals are extracted.  Many of these places are poor and have little in the way of environmental regulation, thus shifting the burden of the environmental costs from wealthy consumers to the impoverished people who live in the vicinity of the mineral production.  That's our choice, that's the trade off for EV.

References

  1. Peterson, J. P., January 2020, U.S. Geological Survey, Mineral Commodity Summaries, Helium,https://pubs.usgs.gov/periodicals/mcs2020/mcs2020.pdf, pp.76-77

  2. Government of Sask., May 28, 2020, Canada’s Largest Helium Purification Facility To Be Built In Saskatchewan, https://www.saskatchewan.ca/government/news-and-media/2020/may/28/helium-facility

  3. Daily Oil Bulletin, Jan. 21, 2021, North American Helium Launching Canada’s Largest Purification Facility in Saskatchewan, https://www.dailyoilbulletin.com/article/2021/1/12/north-american-helium-launching-canadas-largest-pu/

  4. Jaskula, B. W., January 2020, U.S. Geological Survey, Mineral Commodity Summaries, Lithium,https://pubs.usgs.gov/periodicals/mcs2020/mcs2020.pdf, pp 98-99

  5. Hakemon Mike, Apr. 12, 2017, Piercing Lithium Battery (Catches Fire!), https://www.youtube.com/watch?v=xbeQWkYPmfw

  6. Bradley, D.C., Stillings, L.L., Jaskula, B.W., Munk, LeeAnn, and McCauley, A.D., 2017, Lithium, chap. K of Schulz, K.J., DeYoung, J.H., Jr., Seal, R.R., II, and Bradley, D.C., eds., Critical mineral resources of the United States—Economic and environmental geology and prospects for future supply: U.S. Geological Survey Professional Paper 1802, p. K1– K21, https://doi.org/10.3133/pp1802K

  7. Els, F., Jan. 27, 2021, All the mines Tesla needs to build 20 million cars a year, Mining .com, https://www.mining.com/all-the-mines-tesla-needs-to-build-20-million-cars-a-year/

  8. Institute for Energy Research, Nov. 12, 2020, The Environmental Impact of Lithium Batteries,  https://www.instituteforenergyresearch.org/renewable/the-environmental-impact-of-lithium-batteries/

February 15, 2021

Where Does This Stuff Come From?

My previous blog posts discussed  minerals that are either single elements or are compounds of multiple elements. By human standards, the Earth is very large, 5.9724 x 10^24 kg 1.  That is a lot of material.

So where did this stuff come from?

At one time, most people were satisfied with a supernatural explanation,  God or The Gods were responsible for creating the Earth and everything in it.  For people with more important things on their minds, like survival, it was good working hypotheses.  However, some people still asked questions and the answer to the question "where does this stuff come from" eventually was found through one of our oldest scientific pursuits - Astronomy.

The systematic study of the stars probably goes back far in the human past.  However, it wasn't until the 20th Century that we were able to build instruments that could look deep into the far reaches of the Universe.  The discovery of other galaxies by Edwin Hubble in 1925 was followed a few years later by his announcement that the these galaxies were in fact, moving away from each other  2.  

Working back from the observed expansion of the Universe led some people to postulate a "Big Bang"  3 as the origin for the Universe.  So is that the answer? All the 92 elements we have found in nature originated in the Big Bang?

Not quite.  Work by physicists looking at the physics of the fundamental particles of matter 4, led to the discovery that only hydrogen,  helium and some lithium were created  in the Big Bang 5, 6.  The other 89 elements were created through the following processes:

Galactic cosmic ray reactions:
  • Be & B as well as some isotopes of H, He and Li

 Dying low mass stars:
  • Some isotopes of most elements except for Be, B, Tc, and Pm

Exploding  massive stars:
  • Some isotopes of most elements except for H, Li, Be, B, Tc, and Pm

Exploding white dwarf stars:
  • Some isotopes of Si, S, Ar, Ca, Ti, V, Cr, Mn, Fe, Co, Ni and Zn

Merging neutron stars:
  • Some isotopes of Nb, Mo, Ru, Rh, Pd, Cd, In, Sn, Sb, Ce, W and  Re

Radioactive Decay of other Elements
  • The decay of radioactive isotopes produces numerous  elements, most of them unstable. He and Ar are the most common stable elements produced by radioactive decay of other elements. All isotopes  of Tc and Pm are radioactive and decay into other elements.

Figure 1, below, graphically shows the origin of the various elements

So How did this Stuff Form the Earth?

Between the time of the Big Bang, approximately 13.7 billion years ago 3 and the formation of the Earth, 4.54 billion years ago, the stellar processes noted above cooked up most of  the elements and spread them in massive explosions.  The dust of those explosions later coalesced into various  nebulae.  The Sun and planets formed  out of one of these nebulae. 

We are made of star dust.

Figure 2 - Colliding Galaxies
"Colliding Galaxies" by mike.in.ny is licensed under CC BY-NC-SA 2.0

 

References

  1. Williams, D. R., Nov. 2020, Earth Fact Sheet, NASA Goddard Space Flight Center, https://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html 

  2. The Physics of the Universe, 2021, The Expanding Universe and Hubble's Lawhttps://www.physicsoftheuniverse.com/topics_bigbang_expanding.html

  3. The Physics of the Universe, 2021, The Big Bang and the Big Crunch, https://www.physicsoftheuniverse.com/topics_bigbang.html

  4. Weinberg, S, 1993, The First Three Minutes: A Modern View of the Origin of the Universe, 2nd ed., Basic Books, New York NY 

  5. E. Casuso and J. E. Beckman,  Jan. 1997, Beryllium and Boron Evolution in the Galaxy, The Astrophysical Journal, Volume 475, Number 1, https://iopscience.iop.org/article/10.1086/303503/meta 

  6. Kobayashi, C., A. I. Karakas, and M. Lugaro, June 2020, The Origin of Elements from Carbon to Uranium, Astrophysical Journal, The Astrophysical Journal, Volume 900, Number 2, https://arxiv.org/abs/2008.04660 

  7. Cosmos, Sept. 2020, Origin of the elements reviewed, https://cosmosmagazine.com/space/astrophysics/origin-of-the-elements-reviewed/










February 8, 2021

Iron and the Great Oxygenation Event

Figure 1 - Iron Forge

"Forge" by arbyreed is licensed with CC BY-NC-SA 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by-nc-sa/2.0/

Iron in History

Last week's blog entry finished with the Bronze Age collapse.  Following the Bronze Age ca. 1200 B.C., historians generally place the beginning of the Iron Age. 

One of the earliest known uses of iron was a dagger made for Pharaoh Tutankhamen and buried in his tomb 1.  Elsewhere in the Near East,  there is evidence of experimentation with iron as early as 3,300 B.C.,  but it was during the period following the end of the Bronze Age, ca. 1200 B.C. that iron production gradually developed 2.  By 600 B.C., the Iron Age was well underway 2.   Centres of early iron production include the Levant, Anatolia and Cypress 2.  Iron was in use in India by 1,000 B.C 3 and in China, iron was being produced by 700 B.C. 4.  In the period between 800 and 500 B.C., iron use spread throughout Western Europe 5.  In North America, people of the Thule Culture, ancestors to the modern Inuit, are reported to have used iron from meteorites prior to 1000 A.D. 6.

In modern times, iron is built into the fabric of our society.  From household appliances, to steel framed buildings, to bridges, to motor vehicles, to railways and ships, iron (and its alloy, steel) is used in massive quantities by modern civilization. The use of iron, and its production, is therefor one of the marks of the Industrial Age.

Producing Iron

Producing iron from iron ore is essentially a process of chemical reduction whereby the iron ore, largely some form of iron oxide, is heated with a carbon source, such as coked coal, and a flux, such as limestone 7.  In ancient times, bog iron, an iron hydroxide concretion was commonly used as iron ore 8.  In modern times, most iron ore originates in banded iron formations 9.

 

Figure 2 Banded Iron Formation, Soudan, Minnesota

"Jaspilite banded iron formation (Soudan Iron-Formation, Neoarchean, ~2.722 Ga; Stuntz Bay Road outcrop, Soudan Underground State Park, Soudan, Minnesota, USA) 31" by James St. John is licensed under CC BY 2.0


Banded Iron Formations and the Great Oxygenation Event

The most common source of iron ore nowadays is from banded iron formations.  Banded iron formations are biochemical precipitates consisting of layers of iron rich sediment interbedded with siliceous material.  Most of the banded iron formations in the world were deposited during the Great Oxygenation Event at the beginning of the Proterozoic  Eon, 2,460 to 2,426 million years ago 10.

The Great Oxygenation Event was a time in the history of the earth when cyanobacteria (a.k.a. blue green algae) evolved photosynthesis and began releasing free oxygen into the atmosphere .  The basic story is that the free oxygen combined with the dissolved iron in the ocean leading to the deposition of banded iron formations.

Sounds about right, doesn't it?

The problem is in the details of the mechanism of deposition.  Was the deposition  biological or abiotic?  Where did the iron come from?  What about all that silica, how did it get there?  What was the exact mechanism for deposition of the iron and silica? 9,10,11, 12

One of the problems is that there are no modern analogies to the late Archean, early Proterozoic environments.  We are trying to understand what happened in the shift from a reducing environment to an oxidizing environment on a planetary scale.  Clearly the banded iron formations record a dramatic shift in the Earth's environment, but the details are still under investigation 9, 10, 11, 12

Jelte P. Harnmeijer of the University of Washington concluded that "I can only say that the guy responsible for the cliché: “what you don’t know can’t hurt you” probably came up with it after a long and unhappy life spent attempting to understand Banded Iron-Formations"12.

There is a good video on YouTube from December 2020 called How Bad Was the Great Oxygenation Event that's worth watching for an easy summary of the events of late Archean and early Proterozoic eons. also, if this subject intrigues you, follow up on the references below.

References

1.       Comelli, d. et al, May 2016, The meteoritic origin of Tutankhamun's iron dagger blade, Meteoritics & Planetary Science, Vol. 51, Is. 7, July 2016, pp.1301-1309, https://onlinelibrary.wiley.com/doi/full/10.1111/maps.12664?dom=pscau&src=syn

2.       Erb-Satullo, N.L., 2019, The Innovation and Adoption of Iron in the Ancient Near East. Journal of  Archaeological Research Vol. 27, pp. 557–607, https://doi.org/10.1007/s10814-019-09129-6

3.       Chakrabarti, D.K., 1992, The Early Use of Iron in India, Oxford University Press, Oxford U.K.

4.       Young, S.M.M. et al, 2019, The Earliest Use of Iron in China, in Metals in Antiquity, Oxford: Archaeopress, pp. 1-9., http://donwagner.dk/EARFE/EARFE.html

5.       Cunliffe, B. W., 2008, Europe Between the Oceans, Yale University Press, New Haven CT, pp. 270 - 316

6.       Colligan, E., 2017, Thule Iron Use in the Pre-contact Arctic, Ph.D. dissertation, City University of New York, https://academicworks.cuny.edu/gc_etds/2342/

7.       LibreTexts, Aug.2020, Iron Production, https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Modules_and_Websites_(Inorganic_Chemistry)/Descriptive_Chemistry/Elements_Organized_by_Block/3_d-Block_Elements/1b_Properties_of_Transition_Metals/Metallurgy/The_Extraction_of_Iron/Iron_Production

8.       Wikipedia, 2021, Bog Iron, https://en.wikipedia.org/wiki/Bog_iron

9.       K.A. Evans K.A., et al, Feb. 2013, Banded iron formation to iron ore: A record of the evolution of Earth environments?, Geology,  Geology, 41(2)pp. 99- 102, https://www.researchgate.net/publication/256199273_Banded_iron_formation_to_iron_ore_A_record_of_the_evolution_of_Earth_environments

10.   Gumsley, A. P. et al, Feb. 2017, Timing and tempo of the Great Oxidation Event, Proceedings of the Natural Academy of Sciences of the United States of America, vol. 114, no. 8, pp. 1811–1816 https://www.pnas.org/content/114/8/1811

11.   Weiqiang Li, Brian L. Beard, and Clark M. Johnson, 2015, Biologically recycled continental iron is a major component in banded iron formations, Proceedings of the Natural Academy of Sciences of the United States of America, vol. 112, no. 27, pp. 8193–8198, https://www.pnas.org/content/112/27/8193

12.   Harnmeijer, J.P., Mar. 2003, Banded Iron-Formation: A Continuing Enigma of Geology, University of Washington, https://web.archive.org/web/20060908034327/http://earthweb.ess.washington.edu/~jelte/essays/BIFs.doc





February 1, 2021

Copper, Tin, Bronze and the Bronze Age

Copper and tin are significant metals  both in current use and in history.  Alloying nine parts copper with one part tin makes bronze, an extremely useful metal.  The discovery and use of bronze defined an important stage in the human story that we now call the Bronze Age. 

Below, I'll briefly describe the geology of copper and tin deposits and then talk about the Bronze Age.

Copper Geology

Copper is sometimes found in nature as native copper but more often as a component of the sulfide mineral, chalcopyrite.  Weathering of chalcopyrite can lead to the formation of minerals such as chalcocite, bornite, djurleite, malachite, azurite, chyrsocolla, cuprite, tenorite, and brochantite. 1

Copper ores are found in a variety of geological environments.  Chalcopyrite is usually found in volcanogenic environments, such as porphyry copper deposits.  Weathering  and/or  diagenesis of the volcanogenic  rock can lead to the concentration of copper minerals in sedimentary and metamorphic rocks. 2

Tin Geology

The primary ore of tin is the mineral cassiterite.  Cassiterite is an oxide of tin and is considered to be part of the rutile group.  Cassiterite is formed in very light coloured (highly felsic) granites and in pegmatitic veins.  Erosion of these rocks leads to cassiterite accumulating in placer deposits.  These placer deposits are a major source of tin.  3

The Bronze Age

The use of copper preceded the use of bronze. People began using copper as early as the sixth millennium B.C. By 5,100 B.C.  Copper mining was under way in what is now Bulgaria and Spain.  Copper from these locations was traded throughout Europe. During the Bronze Age, Cypress was a major source of copper.

Around the same time that people in Europe were experimenting with copper, native copper was being mined in the Upper Peninsula of Michigan and traded throughout the eastern woodlands of North America. 5

The idea of alloying copper with other metals probably occurred to many artisans in many places. The earliest bronze appears to have been made in what is now Serbia, during the 5th millennium B.C. ; from there the use of bronze spread to Egypt by  3,100 B.C., and to China by 3,000 B.C   6.  By 2,100 B.C. its use had spread to the British Isles  4

Figure 1 shows what casting bronze looks like.

Figure 1 Bronze Casting,  

Credit:  Hans Splinter "bronze casting (1)"  by hans s is licensed with CC BY-ND 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by-nd/2.0/

During the Bronze Age, warrior elites monopolized the use of bronze for weapons and armour.  These elites took over existing states and helped form new ones in the Middle East, Greece and East Asia.  Warrior elites armed with bronze also dominated the chieftainships that existed outside the civilized states.  Bronze became an important commodity in the trade networks.  For example, a flourishing trade network developed among the states of the Eastern Mediterranean, with all sorts of goods travelling from Egypt to the Levant, Anatolia, Cypress  and Mycenaean Greece 7.  However, bronze was the key commodity.

The Bronze Age marked a great advance in the human story.  It was a violent time. They weren't making weapons and armour just for show.  Bronze Age states and minor polities engaged in wars from as far west as the British Isles to the Far East of Shan Dynasty China.

The end of the Bronze age was also marked by violence. The famous siege of Troy, immortalized in Homer's epic poem, The Iliad, was only one of many violent incidents at the end of the Bronze Age.  It is more than just a story of "those who live by the sword shall perish by the sword".  The end of the Bronze Age around the year 1,200 B.C. appears to have been  a systemic collapse caused by multiple social, political and ecological factors 7, 8.

Systemic collapses usually begin with a ecological stress, such as bad weather that leads to crop failures.  The population that could be sustained in the good times is now too big to be fed by the resources available during lean years . Consequently, a series of bad harvests will lead to social and political stress.  Political and economic relationships will be tested and many will fail.  Long established networks of trade may collapse as the goods that were to be traded are no longer available and the trust that bound the system together evaporates. Ambitious warlords arise who motivate desperate people to join them in raiding supposedly richer neighbours.  The onslaught of armed migrants leads to the collapse of now fragile political structures.  After the dust settles, the fires burn out and the bodies buried, a new dark age begins and the survivors find new ways to live.

It's happened before, don't think it can't happen again.

For further reading, begin with the references listed below.

References

  1.  Mineralogical Society of America, 2021, Important Ore Minerals http://www.minsocam.org/msa/collectors_corner/article/oremin.htm 

  2. Toutelot, E. B., & J. D. Vine, 1976, Copper Deposits in Sedimentary and Volcanic Rocks, Geological Survey Professional Paper 907-C, United States Geological Survey, https://pubs.er.usgs.gov/publication/pp907C 

  3. Stanton, R. L., 1972, Ore Petrology, McGraw Hill Book Company, Toronto ON

  4. Cunliffe, B. W., 2008, Europe Between the Oceans, Yale University Press, New Haven CT 

  5. Cullen, K.M., 2006, Milwaukee Public Museum, Old Copper Culture, https://www.mpm.edu/research-collections/anthropology/online-collections-research/old-copper-culture 

  6. Vuckovic, Jan. 2021, The Bronze Age - A Spark That Changed the World, https://www.ancient-origins.net/history-important-events/bronze-age-0013179 

  7. Cline, E. H., 2014, 1177 B.C., the Year Civilization Collapsed, Princeton University Press, Princeton NJ

  8. Chew, S. C., 2007, The Recurring Dark Ages, Altamira Press, Toronto ON


January 25, 2021

Platinum Group Metals

Introduction

In this week's blog, I am going to discuss platinum and the platinum group metals (PGM). PGM are generally considered to be platinum, palla­dium, rhodium, ruthenium, iridium, and osmium.  These metals tend to occur together in nature and have similar physical and chemical properties.

PGM  elements are rare.  The Earth’s upper crust contains only about 0.0005 part per million (ppm) platinum and less of the the other PGM.  Ores that are mined for PGM typically contain 5 to 15 ppm of PGM. 1

While PGM occur as native metals, they also occur as mineral compounds with other elements such as copper, iron, mercury, nickel, silver, bismuth, lead, and tin, antimony, arsenic, tellurium, selenium and sulfur. More than 100 minerals contain one or another PGM as an essential element. Native PGM usually occur as alloys of platinum, iron, osmium and/or iridium. 1

 PGM have many uses:

·         In automobiles: pollution control catalyst, spark plugs, engine control sensors, airbag initiators, electronics for engine management systems, and fuel cells for electric vehicles

·         In electronics: Connectors, Printed Circuits, Resistors, Capacitors, Lasers

·         In computer hard discs, a thin layer of PGM is used to increase memory storage capacity

·         In jewelry and non circulating coinage

·         In glass fibre, display glass, optical glass, ceramic glass, tableware decorative patterns and finishes

·         In health care for antitumor drugs, implants, treatments for heart disease, cancer screening, dental inlays,              crowns and bridges

·         In petrochemicals, as catalysts for production plastics, polyester, pharmaceutical ingredients, high octane              gasoline, fertilizers and explosives, and  silicones

·         In turbine blades for aircraft engines      2

 

Occurrence and Production

PGM can be found in:

·         Magmatic intrusions i.e. mafic and ultramafic intrusions;

·         hydrothermal deposits;

·         sedimentary deposits;

·         residual deposits from weathering; and

·         placer deposits.                                1 

Figure 1 shows the worldwide distribution of magmatic PGM deposits

Figure 1 - PGM Intrusive Deposits 1


World production Figures are shown on Table 1:

Platinum as Money

Like gold and silver, many people look to buying platinum both as an investment and a store of value.  Current prices for platinum are in the order of 1,100 USD/oz.  Over the past year, the prices have ranged from a low of 588 USD/oz in March 2020 to a high of 1,119 USD/oz at the end of the year. 4

As a precious metal, platinum could be used as money, although it lacks the traditional authority of gold and silver.  Imperial Russia issued platinum coins for general circulation from 1825 to 1845 5. Mints that currently issue platinum coins as collector's items include those of Australia, Canada, South Africa, the United Kingdom and the United States.  Precious metals dealers also sell platinum bullion for investors /collectors.  If this interests you, dear reader, do your own homework before you decide to invest; do not follow the advice of random web bloggers.

One interesting tale about platinum coins began in 1992 in the United States with a presidential candidate for the Populist Party, Bo Gritz. Mr. Gritz proposed that the American Congress should authorize the US Treasury  to mint platinum coins in large denominations in order to pay off the US national debt.  In May 2010, a web blogger, Warren Mosler, writing under the nom de plume of Beowulf, popularized the idea and the Nobel Prize winning economist Paul Krugman endorsed it in January 2013.  6

The idea has generally lost favour as people realized that while it may be legal, it amounts to no more than a shift of the debt from one set of financial instruments to another, i.e.from government bonds to government minted coins.  Regardless of the financial legerdemain, the debt is still there. 

References

  1. Zientek, M.L., Loferski, P.J., Parks, H.L., Schulte, R.F., and Seal, R.R., II, 2017, Platinum-group elements, chap. N of Schulz, K.J., DeYoung, J.H., Jr., Seal, R.R., II, and Bradley, D.C., eds., Critical mineral resources of the United States—Economic and environmental geology and prospects for future supply: U.S. Geological Survey Professional Paper 1802, p. N1–N91, https://doi.org/10.3133/pp1802N

  2. The International Platinum Group Metals Association, 2017, Production and Uses of Platinum Group Metals, https://ipa-news.com/assets/sustainability/IPA_Guidance/Chapter%203_PGM_Guide.pdf

  3. U.S. Geological Survey, January 2020, Mineral Commodity Summaries, Platinum Group Metals, https://pubs.usgs.gov/periodicals/mcs2020/mcs2020.pdf

  4. Kitco, January 2021, Live Platinum Price, https://www.kitco.com/charts/liveplatinum.html

  5. Vasilita, S, 2020, History Russian Platinum Coins, Coins Auction, https://www.coins-auctioned.com/learn/coin-articles/history-russian-platinum-coins

  6. Wikipedia, January 2021,Trillion-dollar coin, https://en.wikipedia.org/wiki/Trillion-dollar_coin

January 18, 2018

Gold, Silver & Money

In this blog I will discuss the precious metals, gold and silver, where they occur, how are they produced  and the issue of whether or not they can still be considered money.

Gold Occurrence

In nature, most gold (Au) is almost always found as either native gold or as part of a naturally occurring alloy such as the gold/silver alloy called electrum.  Gold rarely forms compounds with other elements; the twenty or naturally occurring compounds that contain gold are relatively rare.  

Gold deposits are found as either:

  • Lode deposits such as native gold in quartz veins or disseminated gold in sulfide deposits

  • Placer deposits where the gold is found as either dust or nuggets. 1

Gold is extracted from placer deposits using mechanical extraction techniques, such as panning and sluice boxes, to concentrate the gold and other dense minerals. The gold is then removed from the concentrate using chemical extraction techniques.

Separating gold from a lode deposit begins with pulverizing the ore in a mill, followed by mechanical separation of a concentrate containing gold and other dense materials. The gold is then separated from the concentrate using  chemical extraction techniques.

The extraction techniques used for gold concentrates from either placer or lode deposits often include the use mercury or cyanide.  (A good summary can be found in the Encyclopedia Britannica entry on Gold Processing  2).

Silver Occurrence

In  addition to native silver (Ag) there are about 143 minerals that have silver as a significant component 3.  Most of these Ag-bearing minerals are rare except for acanthite, proustite, and pyrargyrite.  Silver also commonly occurs found as a minor constituent of copper, lead, and zinc sulfide minerals or as minor inclusions of native silver within the deposits.  Most silver production is as a by-product of copper, lead and /or zinc production.  4

Silver- bearing minerals are usually found in locations associated with past magmatic activity and/or hydrothermal activity. Deposits of significant grade are formed in four genetic groups:

  1. volcanogenic massive sulphide deposits,

  2. sedimentary exhalative deposits

  3. lithogene deposits, and

  4. magmatic-hydrothermal deposits.    5

 In the Americas, silver deposits are commonly found along the trend of the  western Cordillera from the Andes Mountain Range to Mexico, the United States, Canada and Alaska.  In Europe there is a similar trend of current and ancient volcanic activity that passes from Spain in the west into Turkey in the east.  4

Because silver is mostly produced as a by-product of other metallic mineral production, the methods for extracting silver from the ore will depend on the primary metals in the deposit.  Generally, the ore will be crushed and then smelted and/or chemically treated to separate the silver from the other constituents in the ore. (A good summary can be found in the Encyclopedia Britannica entry on Silver Processing  6)

Is it Money?

The use of gold and silver as currency for trade appears to have begun about 5,000 years ago in Mesopotamia. Until the middle of the twentieth century, gold and silver were normal parts of the money supply.  Gold was often used to settle large, especially international accounts and silver was used in everyday coinage. After the United States went off the gold standard in 1973, most other nations followed suit.  Similarly, in the latter half of the 20th century, silver coins were gradually replaced with coins made out of base metals such as nickel.  Silver dollars were last issued in Canada for normal circulation (as opposed to collectors items) in 1967.  It appears that the story of gold and silver as money is over.

Or s it?

 Our current system of money can best be described as a consensual hallucination in that we all agree that these pieces of paper, book-keeping entries and computer algorithms are worth something.  The value of our money is intimately connected to the power and authority of the governments that issue the currency and decree its value by fiat.  But what happens if trust in the consensual hallucination of fiat currency fails?

Many people who keep gold and silver do so as a hedge against currency instability. Often you will hear them make the following claim: 

"Gold is currency of kings, silver is the currency of free men, barter is the currency of peasants and debt is the currency of slaves." 

The thinking  goes that if the value of fiat currencies drops too much, then gold and silver will be the only acceptable currency.  The problem with this line of thinking is that currency instability is often accompanied by social and political instability.  Ultimately, the value of money depends on the stability of the community that maintains the consensual hallucination, i.e.  that links "money" to the value of things we objectively need or want such as food, clothing, shelter, transportation, fuel and social status.

We may want to ponder the fact that one of the reasons we know a lot about Roman currency is that when the Western Roman Empire was falling apart, wealthy families buried their hordes of gold and silver.  After the barbarians war bands came and went, many of the owners of the buried treasure did not, or could not, return to retrieve their stashes, as in Figure 1.

Figure 1 - Roman silver coins 7

The day may come that gold and silver will again be used as money in response to social and political instability and/or a collapse of trust in government sponsored  fiat currency.  Hopefully, it won't be accompanied by the return of barbarian war bands and a new Dark Age.

References

  1. King, H. M., 2020, Gold, Mineral Properties and Geologic Occurrence,  in Geology.com, https://geology.com/minerals/gold.shtml

  2. Hoffman, J.E and A. Tikkanen, 2008, Gold processing, Encyclopedia Britannica, https://www.britannica.com/technology/gold-processing

  3. Hudson Institute of Mineralogy, 2020, The Mineralogy of Silver, https://www.mindat.org/element/Silver

  4. King, H.M., 2013, Silver, in Geology.com, https://geology.com/minerals/silver.shtml

  5. Graybeal, F. K. and P.G. Vikre, 2010, A review of silver-rich mineral deposits and their metallogeny, Society of Economic Geologists, https://pubs.er.usgs.gov/publication/70194333

  6. Hoffmann, J.E.,2015, Silver processing, Encyclopedia Britannica, https://www.britannica.com/technology/silver-processing

  7. Karasavvas, T., October 2017, Huge Hoard of Ancient Roman Silver Coins Worth £200,000 Found During Treasure Hunt, Ancient Origins, https://www.ancient-origins.net/news-history-archaeology/huge-hoard-ancient-roman-silver-coins-worth-200000-found-during-treasure-021639

January 11, 2021

Deep Time

One of the great contributions by the Science of Geology to our collective store of knowledge was the  discovery of "deep time". The story of the discovery of deep time is fairly complex, involving many people and their work, rivalries, mistakes and the lesson of all their effort. Keep that in mind when reading the brief summary below.

From their study of geology, James Hutton and Charles Lyell both recognized that the earth was probably very old; they just couldn’t find the evidence to give a definitive age 1.  One of the first attempts to calculate an age for the earth from known scientific principles was by William Thomson, Lord Kelvin.  Starting with the assumption that the earth was originally molten and estimating heat transfer from the earth to space, Lord Kelvin believed that the earth was between 20 and 100 million years old 2.

The flaw with Lord Kelvin’s estimate, made in 1863, was that it did not take into account the heat from radioactive decay.  The discovery of radioactive elements by Marie Curie in 1898 lead to further investigations into radioactive minerals by many other researchers.  Thousands of research papers have resulted in an accumulation of knowledge; this in turn has lead to the current estimate that the earth is approximately 4.54 billion years old 3.

A Very Long Time

4.54 billion years is an immense period of time.  To visualize it, imagine a line where every millimetre (mm) represents a thousand years and every metre (m) is a million years.  On this scale, the line representing the total age of the earth will be 4,540 m long.  4,000 m (4 km) of the line represents the length of the Precambrian.  The next 540 m represents the Phanerozoic Eon, the age of complex life.  Approximately 252 million years ago, 252 m on the time line, the Paleozoic ended with the Permian mass extinctions.  66 m from the present on the time line, the Cretaceous ended with the K/T mass extinction.  The entire existence of Homo sapiens, 300,000 years 4, can be represented by 30 cm, a little less than a foot in the old imperial measurement system.  The five thousand years of recorded history amounts to 5 mm and a human life of 80 years equals 0.08 mm on this scale.

Really makes you feel important doesn’t it?

It gets worse, the fossil evidence indicates that most of the species that have ever lived have gone extinct and there is no reason to believe that humans are exempt from this fate 5.

A graphical portrayal of the geological time scale from The Geological Society of America is shown below 6

Living with the Facts

If we hope to benefit from science, then we should adopt an attitude of radical realism.  From our understanding of deep time a couple of lessons stand out:

  • We are the heirs of an immensely long history of life, that history is rich, complex and we are part of it. 

  • We are not as important as we would like to think we are and that is a good thing.

In the end, we are left to ponder lessons of deep time.

References

  1. Gould, S. J., 1987, Time's Arrow, Time's Cycle: Myth and Metaphor in the Discovery of Geological Time, Harvard University Press, Cambridge MA

  2. Lamb, E., June 2013, Lord Kelvin and the Age of the Earth, Scientific American, https://blogs.scientificamerican.com/roots-of-unity/lord-kelvin-age-of-the-eart/  

  3. United States Geological Survey (USGS), July 2007, Age of the Earth, https://pubs.usgs.gov/gip/geotime/age.html 

  4. Science News, September 2017, Modern humans emerged more than 300,000 years ago new study suggests, https://www.sciencedaily.com/releases/2017/09/170928142016.htm 

  5. Quora, March 2015, Why do scientists think that over 99 percent of all species that ever lived have gone extinct?https://www.quora.com/Why-do-scientists-think-that-over-99-percent-of-all-species-that-ever-lived-have-gone-extinct 

  6. The Geological Society of America, Aug. 2018, GSA Geologic Time Scale, Version 5.0, https://www.geosociety.org/GSA/Education_Careers/Geologic_Time_Scale/GSA/timescale/home.aspx

January 4, 2021

What do geoscientists do?

A few years ago, the president of a professional association representing engineers and geoscientists in a Western Canadian province confessed to me that she did not know what geoscientists actually do. I'll try to answer that question here.

There are four main areas of geoscience:

  1. Mineral Exploration and Development

  2. Geophysics

  3. Environmental Geology

  4. General Geology

Mineral Exploration and Development

This is what most people think about  (if they think about it at all) when they hear the word geologist. Mineral exploration and development can be broken down into the following subcategories:

Metallic Minerals: also called "hard rock"geology.  Geoeoscientists who work in this area explore and help develop mines for materials such as gold, silver, copper, platinum group metals, copper, zinc, lead, uranium, aluminum and any other metal that has a market value.

Fossil Fuel Minerals:  also called "soft rock" geology. Geoscientists who work in this area explore for petroleum, natural gas and coal.  

Industrial Minerals and Aggregates: these include a wide variety of minerals and materials such as metal oxides used for pigments, gypsum for drywall, clay for ceramics, crushed stone, dimension stone, and especially sand and gravel.  In terms of sheer volume of materials, sand and gravel make up the largest mined products in the world. In fact the amount of sand and gravel moved by people approaches the amount of material moved by rivers through normal erosion.

Geophysics

Geophysics is the area of geoscience concerned with the physical processes and physical properties of the Earth.; as such, it includes the following areas:

Seismology: this is the study of earthquakes and earth movements and includes the general field of Plate Tectonics.

Instrumentation: this includes the development and use of instruments to measure gravity, magnetism, heat flow and and other properties.  I also includes electromagnetic imaging of the subsurface. Geophysical instrumentation is a huge area area of study.

Environmental Geology

Environmental geology includes the following:

Contaminated Sites: this is the investigation and remediation of properties that have been adversely affected by human activity.  

Hydrogeology: this is the study of the occurrence, flow and development of groundwater resources

General Geology

The fields of study under this heading are those that often seen as academic but which often have a direct bearing on practical matters. These fields include:

Vulcanology: the study of volcanoes

Quaternary Geology: the study of the Quaternary Period in the geological time scale. This includes the Pleistocene ice ages and the current Holocene Epoch

Engineering Geology: this is the application geology to engineering problems and includes evaluation of hazards such ass earthquakes and landslides.

Historical Geology:  the history of the earth, this includes the study of fossils, Paleontology

Geochemistry: the chemistry rocks and minerals