We all like to think that we're unique, but our planet probably is, at least in terms of its assortment of rare minerals. Those substances represent Earth's truest distinction from other planets, according to scientists who've developed the first system for categorizing rarities in the mineral kingdom.
Scientists Robert Hazen of the Carnegie Institution and Jesse Ausubel of The Rockefeller University, whose research paper will appear in a future issue of the journal American Mineralogist, have inventoried the world's rarest mineral species.
Their database includes 2,550 substances that are far rarer than diamonds and gemstones. Several, in fact, are so scarce that the known supply worldwide would be smaller than a sugar cube. Many are incredibly fragile, with a tendency to melt, evaporate or dehydrate, and a few will decompose if they are exposed to sunlight.
PHOTOS: Rare Minerals We May Have to Live Without
And as the scientists note in their paper, many of the rarest minerals develop as a consequence of biological changes in the Earth's environment. "We suggest that the distribution of rare minerals may not only arise from biological activity, but also may be a robust biosignature of life" on Earth and other planets, they wrote.
Surprisingly, the stuff that we think of as rare often isn't.
"Uses of the word ‘rare' in the context of ‘rare earth elements' or ‘rare metals' are similarly misleading, as many thousands of tons of these commodities are produced annually," the scientists point out. And precious gems are found in numerous places around the world, and are bought and sold in commercial quantities.
NEWS: Could a Carbon-Scrubbing Rock Slow Climate Change?
Diamonds, for example, are found in significant quantities in 11 countries around the world, and the biggest producer, Russia, mined 23,000 tons of them in 2014, according to Geology.com. In contrast, each of the 2,550 rare minerals is found at five or fewer locations worldwide.
Perhaps the rarest mineral is ichnusaite, created from a combination of the radioactive element thorium and lead-like molybdenum underground. Only one specimen has ever been found, in Sardinia back in 2013. And Nevadaite, a combination of vanadium and copper, has been found only in Nevada and Kyrgyzstan.