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from the if-god-isn't-real-who-tricks-scientists? dept.
Scientists long believed that Earth's lower mantle was composed of Bridgmanite (Mg,Fe)SiO3 and magnesiowüstite (Mg,Fe)O, in which Fe2+ dwells. This view changed when experiments showed that Fe2+ simply can't exist at the pressure and temperature of the lower mantle. What is present is Fe3+. The two phases (Mg,Fe)SiO3 and (Mg,Fe)O both shed Fe2+ and, in turn, MgSiO3 and MgO remain. However, what mineral hosts Fe3+ had remained unknown.
Now, scientists have a possible answer: Maohokite, a newly discovered high-pressure mineral. It may be what composes the Earth's lower mantle along with Bridgmanite MgSiO3 and magnesiowüstite MgO. The study reporting this new mineral was published in Meteoritics & Planetary Science.
[...] Maohokite, with a composition of MgFe2O4, has an orthorhombic CaFe2O4-type structure. The existing mineralogical model of the Earth's mantle shows that the ferromagnesian lower mantle is mainly composed of Bridgmanite (Mg,Fe)SiO3 and magnesiowüstite (Mg,Fe)O. Therefore, the fact that Maohokite contains Mg and Fe, two major components of the lower mantle, only makes the case stronger that Maokohite is a key mineral in the lower mantle.
The researchers were under a lot of pressure to produce this result.
(Score: 2) by dltaylor on Saturday December 08 2018, @10:16AM
AFAIK, they use small diamond anvils and lasers to produce the pressures and temperatures presumed to exist at various layers of the mantle (the layers correspond to phase changes in the materials at various temperatures and pressures; material "A" exists within this range and material "B" exists within some other range).
How sure can they be that materials existing in the very small test cells correspond to the much more mixed and distributed environments of kilometers deep and fluid environments of the mantle?
Of course, there's an apropos XKCD: https://xkcd.com/2058/ [xkcd.com]