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Mineral Diversity

August 22, 2022

For much of my career, I was involved in X-ray X-ray crystallography and the growth of magnetic, optical, and piezoelectric crystals, as were many of my colleagues. Many of these colleagues were inspired in their choice of profession by a childhood interest in mineralogy, and many of them had large mineral collections, often displayed in showcases their homes. At the same time that I was spending too much money on electronic components, they were spending about the same amount on unique mineral specimens. Interestingly, American financier, John Pierpont (J. P.) Morgan (1837-1913), had an extensive gem collection, and the mineral, morganite, is named in his honor.

A specimen of morganite, recovered from a mine in the Southeast Region of Brazil.

Morganite, like emerald, is a crystal of beryllium-aluminum-silicate, beryl (Be₃Al₂(SiO₃)₆).

Cr³⁺ dopant gives emerald its green color, while Mn²⁺ dopant gives morganite its pink color.

Beryl minerals are formed in nature by hydrothermal growth, and this technique is used to produce synthetic versions. A carat of morganite costs several hundred dollars, an order of magnitude less than diamond.

(Wikimedia Commons image by Robert M. Lavinsky. Click for larger image.)

Modern crystal growth technology has the capability of making synthetic versions of minerals found in nature, including the once elusive diamond, often with greater perfection. The first solid state laser, a ruby laser created in 1960 by Theodore "Ted" Maiman (1927-2007), used a synthetic ruby crystal. Ruby is chromium-doped sapphire, and titanium-doped synthetic sapphire is used for tunable lasers. While excellent quality gems are produced synthetically, gem marketers insist that consumers should buy natural crystals, since they're the real thing.

The prolific Robert M. Hazen and colleagues have been cataloging Earth's minerals for many years. I wrote about some of their research in two previous articles (Anthropocene Minerals, August 16, 2021 and Earth's Mineral Wealth, October 19, 2015. A mineral is completely specified by its chemical composition and crystal structure, but a recent article has examined the many ways that such minerals are formed.[1-2] For example, iron pyrite, commonly called fool's gold is formed in nature in 21 ways, the most of any mineral. Diamonds are formed in nine ways in places like outer space and deep within the Earth.

A mineral specimen of iron pyrite, "fool's gold," the mineral type with the greatest diversity of origin.

Since the birth of the Solar System, about 4.5 billion years ago, nature has used 21 different ways to create pyrite. Pyrite forms at low and high temperatures, with and without water.

Pyrite formation can be helped by microbes, but it is found also in harsh environments where life is not present.

(Photo by ARKENSTONE/Rob Lavinsky. Click for larger image.)

The paper, published in American Mineralogist, is a culmination of a fifteen year study led by the Carnegie Institution for Science to detail the origins and diversity of every known mineral.[2] The research team built a database of every process of formation of every known mineral, and it included information from the open access mineral databases, mindat.org and rruff.info/ima) as well as information from thousands of primary geology and mineral research articles.[2]

While there are about 6,000 mineral species identified by their chemical composition and crystal structure, the researchers identified 10,556 different combinations of minerals and modes of formation, what they call mineral kinds.[1-2] Nature has used 57 processes to create these mineral kinds.[2] Minerals with 15 or more known modes of formation are pyrite, albite, hornblende, corundum, magnetite, calcite, hematite, rutile, and baryte.[1]

A specimen of the mineral, beryl (Be₃Al₂(SiO₃)₆).

Beryl is the most common mineral containing the element, beryllium. Morganite, as shown in the first figure, is also a beryl.

(Photo by ARKENSTONE/Rob Lavinsky. Click for larger image.)

The research team found that 40% of Earth's 5,659 recognized mineral species were created in more than one way, and the nine listed above were created in 15 or more ways.[1-2] The diverse processes for mineral creation range from instantaneous lightning and meteor strikes, to hydrothermal synthesis spanning hundreds of millions of years.[2] At least 4583 minerals, 81% of all mineral species, have been formed hydrothermally.[1] Lack of water explains why the Moon, Mercury and Mars have far fewer mineral species than Earth.[2] One-third of minerals owe their creation to biological processes, and biology has an indirect role through the creation of Earth's oxygen-rich atmosphere and 2,000 minerals that wouldn't have formed otherwise. [2]

An opalized fossil specimen of an ammonite, a species of the class, Cephalopoda, from Alberta, Canada.

This illustrates the intersection of minerals and life.

I wrote about ammonites earlier in the year (The Largest Ammonite, January 10, 2022)

(Photo by ARKENSTONE/Rob Lavinsky. Click for larger image.)

There are 296 minerals thought to pre-date Earth, and 97 are known only from meteorites, some of these dated as created 7 billion years ago, before the creation of the Solar System.[2] The oldest terrestrial crystals are zircons, first created 4.4 billion years ago.[2] There are more than 600 minerals created as a result of human activities, including more than 500 caused by mining, and 234 from coal mine fires.[2] There are 77 biominerals that are formed by biological processes, such as those present in corals, shells, bones, teeth and kidney stones.[2] Seventy-two minerals derive directly or indirectly from the guano and urine of birds and bats, including the rare mineral spheniscidite, a phosphate mineral formed when the urine of penguins reacts with clay minerals beneath a rookery on Elephant Island off the coast of Antarctica.[2]

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