Natural Occurrence of MgSiO3-Ilmenite and Evidence for MgSiO3-Perovskite in a Shocked L Chondrite

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Science  18 Jul 1997:
Vol. 277, Issue 5324, pp. 352-355
DOI: 10.1126/science.277.5324.352

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Shock-induced melt veins in the Acfer 040 L5-6 (S6) chondrite contain a previously unknown set of high pressure phases consisting of amorphous grains similar in composition to majorite, MgSiO3-ilmenite, and ringwoodite. The amorphous grains have compositions that are similar to those of synthetic MgSiO3-perovskites from chemically complex systems and are inferred to be MgSiO3-perovskite that crystallized from the melt at high pressure and temperature and subsequently amorphized after pressure release. The ilmenite represents a natural occurrence of a potentially important mineral in Earth's mantle. The MgSiO3-perovskite–MgSiO3-ilmenite–ringwoodite assemblage is not predicted by phase equilibria studies, but appears to result from crystallization of a melt at pressures above 26 gigapascals.

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