A 15-year study 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.
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 (lumping) kindred species of minerals together or splitting off new species 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% greater than the roughly 6,000 mineral species recognized by the International Mineralogical Association (IMA) on the basis of crystal structure and chemical composition alone.
"This work fundamentally changes our view of the diversity of minerals on the planet," says Dr Hazen, Staff Scientist with the Earth and Planets Laboratory, Carnegie Institution for Science, Washington DC.
80% of Earth's minerals were mediated by water
"For example, more than 80% 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."
40% of Earth's mineral species formed in more than one way
According to the paper, nature created 40% of Earth's mineral species in more than one way -- for example, both abiotically and with a helping hand from cells -- and in several cases used more than 15 different recipes to produce the same crystal structure and chemical composition.
Of the 5,659 recognized mineral species surveyed by Hazen and colleagues, nine came into being via 15 or more different physical, chemical and/or biological processes -- everything from the 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.
And, as if to show she has a sense of humor, Nature has used 21 different ways over the last 4.5 billion years to create pyrite (aka Fool's Gold) -- the mineral world's champion of diverse origins. Pyrite forms at high temperatures and low, with and without water, with the help of microbes and in harsh environments where life plays no role whatsoever.
Composed of one part iron to two parts sulfide (FeS2), pyrite is derived and delivered via meteorites, volcanos, hydrothermal deposits, by pressure between layers of rock, near-surface rock weathering, microbially-precipitated deposits, several mining-associated processes including coal mine fires, and many other means.
To reach their conclusions, Hazen and Morrison built a database of every known process of formation of every known mineral. Relying on large, open-access mineral databases (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, detailed in the paper, "On the paragenetic modes of minerals: A mineral evolution perspective."
In all, minerals have come into being in one or more of 57 different ways, according to that paper and a sister paper published simultaneously by the same journal, "Lumping and splitting: toward a classification of mineral natural kinds," co-authored by Drs. Hazen and Morrison in collaboration with mineralogists Sergey Krivovichev of the Russian Academy of Sciences and Robert Downs of the University of Arizona.
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."
Distinguishing minerals based on how and when each kind appeared through Earth's 4.5 billion+ year history
In earlier studies over more than a century, thousands of mineralogists worldwide have carefully documented almost 6,000 different "mineral species" based on their unique combinations of chemical composition and crystal structure. Dr Hazen and colleagues took a different approach, emphasizing how and when each kind of mineral appeared through more than 4.5 billion years of Earth's history.
"No one has undertaken this huge task before," says Dr Hazen, honoured by the IMA with its 2021 medal for his outstanding achievements in mineral crystal chemistry, particularly in the field of mineral evolution.
"In these twin papers, we are putting forward our best effort to lay the groundwork for a new approach to recognizing different kinds of minerals. We welcome the insights, additions, and future versions of the mineralogical community."