There are more than 5,000 known minerals on Earth, and most of them are much more rare than Valentine's Day diamonds.
After all, diamonds can be found in more than 700 locations around the world, and miners pull tons of them out of the ground each year.
Compare that to the beautiful Valentine's Day pink mineral cobaltomenite, which is found in just four places: Argentina, Bolivia, the Democratic Republic of Congo and Utah.
Scientists say there is so little cobaltomenite on our planet that you could probably fit it all into a container the size of a shot glass.
Now that's a rare mineral.
In a paper to be published in American Mineralogist, two researchers present the first system for categorizing rarities in the mineral kingdom by suggesting four reasons that a mineral might be hard to find.
They explain that some minerals can only form under very specific pressures and temperatures, while others are formed of rare elements that are almost never found in the same place at the same time.
Some minerals are ephemeral; they dissolve in rain or decompose in the sun. Others can only be found in places that are extremely hard to get to, like the edges of volcanoes or the deepest parts of the ocean.
One of the rarest known minerals on the planet is fingerite, which has only been seen near the summit of the Izalco volcano in El Salvador. Reserchers call it the "perfect storm of rarity" because it is made of rare elements, it dissolves in the rain, and it only forms under specific conditions that occur near active volcanoes.
Studying rare minerals can help scientists better understand the extreme pressure and temperature conditions that exist on the planet, as well as the role that life plays in the creation of Earth's mineral mix, said mineralogist Robert Hazen of the Carnegie Institution in Washington and one of the authors of the work.
"What is most astonishing about rare minerals is that the processes that ultimately forms most of them comes from biology," he said. "As life changes near the surface of our planet, it creates new conditions that leads to the creation of thousands of new minerals."
One of those minerals was named for Hazen -- the delicate and fleeting hazenite. (It was discovered by a former student of his.)
Hazenite has only been found in Mono Lake in the California desert, and only on certain days of the year.
When the lake has been dry for a long time, the phosphorous levels occasionally get so high that they start to poison the microbes that live on the lakebed. To deal with the excess phosphorous, these microscopic life forms excrete tiny little hazenite crystals.
"They're basically microbial poop," said Hazen. "People tell me, 'Hazenite happens.'"
Nevadaite has striking blue crystals that are also microscopic. It is made of the scarce elements vanadium and copper, and it has only been found in two places -- Eureka County, Nev., and a copper mine in Kyrgyzstan.
Another of the rarest known minerals is ichnusaite. It was created through a subterranean mash-up of the radioactive element thorium and lead-like molybdenum. Only one specimen has ever been found. That was on the Italian island of Sardinia a few years ago.
In the world of mineralogy, it seems that each mineral has a unique and fascinating story to tell about the vast range of elements and environments on our planet.
For example, in 2014 scientists found a tiny but analyzable sample of a mineral called bridgmanite after searching for it for half a century.
Bridgmanite forms under such high pressure that the only way it could even occur on Earth's surface is if a meteorite struck the planetary crust with an immense force. However, scientists believe that bridgmanite makes up 70% of the lower part of Earth's mantle, where the pressure is much higher.
Last year Hazen and his team put out a paper that predicts there are still 1,500 undiscovered minerals.
At the same time, their calculations suggest that the distinct mineral composition of Earth could not be found anywhere else in the universe.
"Earth's mineralogy is absolutely unique in the cosmos," he said.
Now that's seriously rare.
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