Abstract
Lamellar inclusions of chromian spinel ( Cr/Cr + Al> 0.7), clinopyroxene and chromian spinel-clinopyroxene symplectite occur in olivines from alpine-type peridotites which have equilibrated at relatively low temperature (<700°C). They occur most commonly in dunite with very magnesian olivine (Fo 93 to Fo 95) and discrete grains of Cr-rich spinel. Olivine which initially equilibrated with magnesian and Cr-rich liquid had contained small amounts of calcium and trivalent chromium in the octahedral site, and lamellar chromian spinel and diopsidic clinopyroxene exsolved during the annealing process. The ordinary depletion of chromium or absence of chromian spinel lamellae in olivines in igneous rocks may be partly due to the effective exclusion of chromium from olivine upon cooling.
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