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Science 8 October 1982:
Vol. 218. no. 4568, pp. 152 - 153
DOI: 10.1126/science.218.4568.152
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Articles

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

ANDREW M. ISAACS 1 and DONALD R. PEACOR 2

1 Planetary and Earth Sciences Division, NASA Johnson Space Center, Houston, Texas 77058
2 Department of Geological Sciences, University of Michigan, Ann Arbor 48109

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.

Submitted on April 5, 1982
Revised on June 21, 1982


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Energy-filtered transmission electron microscopy (EFTEM) of intergrown pyroxenes.
K. T. Moore, D. C. Elbert, and D. R. Veblen (2001)
American Mineralogist 86, 814-825
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