POIKILITIC PYROXENE   POIKILITIC PYROXENE
Anorthosite
Piscataquis County, Maine

The orange background is a single crystal of pyroxene that surrounds many rectangular crystals of twinned plagioclase. Both minerals grew from a magma, but this melt contained more seeds of plagioclase than pyroxene. As the magma crystallized, the growing pyroxene captured the more numerous but smaller plagioclase crystals that were floating helplessly in the melt. The resulting pattern is known as a poikilitic texture. Plates of biotite, a mica seen here on edge, cut across both plagioclase and pyroxene, and indicate that biotite grew during the latest stages of crystallization.

Crossed polarizers

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