Olivine-Garnet Transformation in a Meteorite

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Science  05 Apr 1968:
Vol. 160, Issue 3823, pp. 66-67
DOI: 10.1126/science.160.3823.66


Garnet has been identified for the first time as a meteorite mineral in the Coorara chondrite from Western Australia. It replaces olivine grains in a 1-millimeter veinlet traversing the body of the meteorite. The associated olivine has abnormally low birefringence, which suggests a highly shocked condition. Microprobe analyses do not distinguish the garnet from the associated olivine, which has the composition (Mg.75Fe.25)2 SiO4; the garnet may have the composition Mg3Fe2Si3O12 but be unresolvable from the accompanying olivine, or alternatively is nonstoichiometric. Transformation of olivine to garnet under high pressure could have significant implications for the phase composition of the Earth's mantle.

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