Perthite

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, Universityof Wisconsin - Green Bay

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Perthite is the result of exsolution during the cooling of feldspar. Plagioclase and K-feldspar that initially are compatible in solid solution become incompatible and separate. Generally the feldspar consists of a matrix of K-feldspar enclosing irregular patches or bands of plagioclase. The reverse situation, with plagioclase enclosing K-feldspar, is termed anti-perthite.

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Plane-Polarized Light

Clear, low relief, resembles other feldspars. May show dusty inclusions or sericite alteration. Some borders of exsolution domains may be visible.

Crossed Polarizers

First-order gray, mottled, patchy or irregularly striped

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The view below in crossed polarizers is very typical of perthitic texture.

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Created 10 Oct 1997, Last Update