Orthopyroxene Exsolution in Augite: A Two-Step, Diffusion-Transformation Process

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Science  08 Oct 1982:
Vol. 218, Issue 4568, pp. 152-153
DOI: 10.1126/science.218.4568.152


Orthopyroxene lamellae exsolved from augite on (100) are shown to grow by a two-step process involving (i) the diffusion of calcium and (magnesium, iron) to form clinohypersthene and (ii) the inversion of clinohypersthene to orthopyroxene, probably by glide twinning. If complete inversion is prevented by cooling or steep concentration gradients, the two-step process produces orthopyroxene with narrow margins of clinohypersthene. Measured elemental concentration gradients at (100) lamellar interfaces support this mechanism.