Mark Megahan
When Oliver Tschauner’s new mineral was confirmed by the International Mineralogical Association, he earned the right to give it a name. He could have called it “Merlinium” in reference to the Arthurian wizard, once imprisoned in crystal, but he didn’t. Instead he named Davemaoite “after his once-postdoctoral supervisor, Dave (Ho-kwang) Mao, a prominent geophysicist.”
A whole new mineral
Just like the wizard alchemist Merlin, who was once imprisoned in crystal, Tschauner’s new mineral sample is imprisoned within a crystal of solid diamond.
If the pressure were released by cracking it open, the only specimen known to man would magically transform itself into ordinary glass. The diamond, along with it’s calcium, silicon and oxygen inclusion, worked its way to the surface from 550 miles down in the bowels of the Earth.
Davemaoite is a crystal of CaSiO3 Calcium Silicate with a perovskite lattice structure. It’s also “the first compound of its kind to be identified in the lower mantle, the deepest layer of the earth’s geology outside of its core.”
It’s amazing the mineral was spotted in the first place. Oliver Tschauner and his team of researchers had assembled from Nevada, Florida, and California. They were examining the diamond under “powerful x-ray with precision down to the micrometer that can send signals through rocks.”
What they found offers “new evidence of the existence of a mineral that’s been speculated about for years, but never sampled.” The whole process took more than a year. Because we can’t get down to the layer just outside the core, we can’t directly mine the stuff.
“The deep Earth is not directly accessible. We have seismic data, geochemical data from rocks that may have originated there, we can perform experiments at the pressures and temperatures of the deep Earth but we had no actual samples of real minerals from that deep. The inclusions in diamond provide this missing information.”
An ‘unquenchable’ compound
The diamond in which the Davemaoite is trapped was mined in Orapa, Botswana and found its way to the gem and mineral collection of the Natural History Museum of Los Angeles.
As Dr. Tschauner explains, his sample of Calcium Silicate perovskite “is ‘unquenchable,’ meaning it can only maintain its structural characteristics under the high pressure conditions of the lower mantle. The diamond it was found within kept it from changing structure in its travel hundreds of kilometers up to the earth’s outer layers.”
Since that’s “a pressure that is 24,000 times that of the earth’s atmosphere.” it’s a little hard to recreate in the lab.
Tschauner’s priceless mineral sample “would turn into glass instantly in the atmosphere.” They “reconstructed the pressure-temperature path that the diamond and its inclusions took and we concluded that the diamond grew somewhere between 660 and 900 kilometers deep.” That’s pretty far down.
Even in the place where Davemaoite is found occurring naturally, there isn’t much of the stuff, making it one of the rarest mineral specimens in the world. Davemaoite “constitutes five to seven per cent of the earth’s lower mantle.” According to Tschauner, that’s “not much.”
It is important stuff though. It “plays an important role in the overall heat levels of the earth’s interior because it decays radioactively.” That’s crucial because “radioactive decay is responsible for one-third of the inner earth’s heat.”
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