Various gemstones on display in the souk of Marrakesh in Morocco.
A 15-year study led by the Carnegie Institution for Science details the origins and diversity of every known mineral on Earth, a landmark body of work that will help reconstruct the history of life on Earth, guide the search for new minerals and ore deposits, predict possible characteristics of future life, and aid the search for habitable planets and extraterrestrial life.
Approximately 6,000 different naturally occurring minerals, classified based on their unique combinations of chemical composition and crystal structure, are known today.
In twin papers published today by American Mineralogist and sponsored in part by NASA, Carnegie scientists Robert Hazen and Shaunna Morrison detail a novel approach to clustering kindred species of minerals together or splitting off new kinds based on when and how they originated.
Once mineral genesis is factored in, the number of “mineral kinds”—a newly-coined term—totals more than 10,500, a number about 75 percent greater than the roughly 6,000 mineral species recognized by the International Mineralogical Association (IMA).
“This work fundamentally changes our view of the diversity of minerals on the planet,” says Hazen.
“For example, more than 80 percent of Earth’s minerals were mediated by water, which is, therefore, fundamentally important to mineral diversity on this planet. By extension, this explains one of the key reasons why the Moon and Mercury and even Mars have far fewer mineral species than Earth.”
“The work also tells us something very profound about the role of biology,” he adds. “One third of Earth’s minerals could not have formed without biology—shells and bones and teeth, or microbes, for example, or the vital indirect role of biology, such as by creating an oxygen-rich atmosphere that led to 2,000 minerals that wouldn’t have formed otherwise.”
“Each mineral specimen has a history. Each tells a story. Each is a time capsule that reveals Earth’s past as nothing else can.”
In the paper “On the paragenetic modes of minerals: A mineral evolution perspective“, the researchers classified minerals based on the way they can form in nature – by physical, chemical and/or biological processes – everything from near-instantaneous formation by lightning or meteor strikes, to changes caused by water-rock interactions or transformations at high pressures and temperature spanning hundreds of millions of years, or in bones, shells and tissue of animals and plants.
According to the research, 3,349 (59 percent) of minerals are known to occur from just one process, 1,372 species (24 percent) from two processes, 458 (8 percent) from three processes, and the rest, 480 (8 percent), from four or more processes.
Diamonds, for example, composed of carbon, have originated in at least nine ways, including condensation in the cooling atmospheres of old stars, during a meteorite impact, and under ultra-high-pressure deep within the Earth.
In all, minerals have come into being in one or more of 57 different ways, according to the sister paper published simultaneously, “Lumping and splitting: toward a classification of mineral natural kinds,” co-authored by Hazen and Morrison in collaboration with mineralogists Sergey Krivovichev of the Russian Academy of Sciences and Robert Downs of the University of Arizona.
To reach their conclusions, the researchers built a database of every known process of formation of every known mineral. Relying on large, open-access mineral databases (like mindat.org and rruff.ima/info), amplified by thousands of primary research articles on the geology of mineral localities around the world, they identified 10,556 different combinations of minerals and modes of formation.
The mineral world’s champion of diverse origins is the humble pyrite (FeS2), known by many as Fool’s Gold. Pyrite is found in metamorphic rocks, in volcanic deposits, in sedimentary rocks, forms in hydrothermal springs and is deposited by percolating water in abandoned mines. Crystals were found even in meteorites and some animals use this mineral to build their shells.
Sample of the mineral pyrite, also known as, Fool’s Gold.
The other extreme is the rare mineral spheniscidite, which forms only when the urine of penguins (order Sphenisciformes, hence the mineral name) reacts with clay minerals beneath a rookery on Elephant Island in the British Antarctic Territory.
The goal of their efforts: “To understand how the diversity and distribution of minerals have changed through deep time and to propose a system of mineral classification that reflects mineral origins in the context of evolving terrestrial worlds.”
“No one has undertaken this huge task before,” says Hazen, honoured by the IMA with its 2021 medal for his outstanding achievements in mineral crystal chemistry, particularly in the field of mineral evolution – a new field of science that links minerals with the evolution of life on Earth.
This classification could also be used for extraterrestrial minerals. On planets sharing some similarities with Earth, like Mars with its traces of water, one may expect similar minerals as formed under terrestrial conditions. However, on exotic worlds, like the moon Titan with its dense nitrogen atmosphere and methane lakes, one may expect minerals not seen on Earth.
