[Rockhounds] What's the deepest-occurring gemstone on Earth?

[Kreigh Tomaszewski]

In Virgin Valley, Nevada, it's possible to spend an afternoon digging for
rare black fire opals, while visitors to Coalinga, California, can scour
the dirt for pieces of the state's official gemstone, benitoite. At
Arkansas' Crater of Diamonds State Park, aspiring gemhounds pay just $10 to
hunt for the world's most sought-after stones.

Each of these outings requires little more than hand tools, yet most
gemstones originate between *3 to 25 miles (5 to 40 kilometers) belowground*
<https://www.thermofisher.com/blog/mining/where-did-those-gemstones-come-from>,
and some extend far deeper.

But which gemstones are found the deepest, and how do they make their way
to the surface?

According to *Lee Groat* <https://www.eoas.ubc.ca/people/leegroat>, a
mineralogist at the University of British Columbia, the deepest known
gemstones *are diamonds* <https://www.livescience.com/diamonds-facts>,
sought for their beauty, use in industry and the scientific data they
contain.

How diamonds form still isn't entirely understood, but laboratory
experiments show that the gemstones crystallize only under extreme
pressures. Most naturally occurring stones *have been traced to the upper
mantle*
<https://go.redirectingat.com/?id=92X1590019&xcust=livescience_us_3280512064414168000&xs=1&url=https%3A%2F%2Fwww.nature.com%2Farticles%2Fs41561-022-01064-4&sref=https%3A%2F%2Fwww.livescience.com%2Fplanet-earth%2Fgeology%2Fwhats-the-deepest-occurring-gemstone-on-earth>,
at depths between 93 and 186 miles (150 to 300 km), where pressures can
reach beyond 20,000 atmospheres.

https://www.livescience.com/planet-earth/geology/whats-the-deepest-occurring-gemstone-on-earth