17/02/2016 3:13 PM AEDT | Updated 18/02/2016 1:03 AM AEDT

Earth's Rarest Minerals Give Diamonds A Run For Their Money

Some minerals are so rare, the entire Earth's supply is smaller than a sugar cube.

Marilyn Monroe, who famously said, "Diamonds are a girl's best friend," probably hadn't heard of Sardinian ichnusaite.

Ichnusaite, a pearly, colorless and brittle mineral, was discovered on the Italian island of Sardinia in 2013. Mineralogist Robert Hazen says that with only one known specimen, it's a true rarity.

"If you wanted to give your fiancé a really rare ring, forget diamond. Give her Sardinian ichnusaite," said Hazen, co-author of a new paper categorizing Earth's rarest minerals.

Robert Downs/University of Arizona
Ichnusaite is only known to exist on the island of Sardinia, in Italy.

Or maybe go with cobaltomenite, a pink-red mineral found in just four locations -- Utah, Argentina, Bolivia and Congo.

As the Los Angeles Times reports, cobaltomenite is so rare that the Earth's supply could fit in a shot glass.

Robert Downs/University of Arizona
Cobaltomenite is found in just four places on Earth. 

In a study to be published in American Mineralogist, Hazen, of the Carnegie Institution in Washington, and Jesse Ausubel, a scientist at The Rockefeller University, inventoried and categorized more than 2,500 minerals -- the rarest of the rare. Each comes from five or fewer known sites worldwide, and several have a known supply smaller than a sugar cube.

"These 2,550 minerals are far more rare than pricey diamonds and gems usually presented as tokens of love," the authors wrote in a statement.

But there's one major problem for those thinking of putting the rare minerals on a wedding band.

"Several are prone to melt, evaporate or dehydrate," the authors said. "And a few, vampire-like, gradually decompose on exposure to sunlight."

Robert Downs/University of Arizona
Nevadaite is formed from the scarce elements vanadium and copper under very restricted environmental conditions. The crystals are colorful but microscopic, and only known from two localities -- Eureka County, Nevada, and a copper mine in Kyrgyzstan.

While there are more than 5,000 confirmed minerals on Earth, fewer than 100 of them make up 99 percent of Earth’s crust, according to the study. 

It's the rarest ones, Hazen told BBC News, that make Earth special and are "key to the diversity of the Earth's near-surface environments."

In their paper, "On the Nature and Significance of Rarity in Mineralogy," Hazen and Ausubel categorize rare minerals based on the unique conditions that created them, the rarity of their ingredients, how ephemeral, or short-lived, they are, and the extreme, remote locations where they are found.

Robert Downs/University of Arizona
Fingerite, named after mineralogist and crystallographer Larry Finger, is the "perfect storm" of rarity.

A "perfect storm of rarity," Hazen said, is fingerite, known only to exist near the summit of Izalco Volcano in El Salvador.

"It's made of rare elements -- vanadium and copper have to exist together, and it forms under an extremely narrow range of conditions," Hazen told BBC News. "If you just change the ratio of copper to vanadium slightly, you get a different mineral. And every time it rains, fingerite washes away."

So, basically, if you're hoping for a dark-red hunk of cobaltomenite or a piece of nevadaite next Valentine's Day, keep dreaming.

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