Geological Glossary

Glossary of common terms used in geology, and related to earth sciences.

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Feldspar

Plagioclase feldspar Plagioclase is a member of the feldspar mineral family. Plagioclase feldspars are yet another silicate that contains considerable sodium or calcium. Feldspar crystals are stubby prisms, generally white to gray and a glassy luster. This variety of plagioclase, called albite, is rich in sodium.

Potassium feldspar Potassium feldspar is another member of the feldspar mineral family. Like plagioclase feldspar, potassium feldspars are silicate minerals that contain a considerable amount of -you guessed it- potassium. Feldspar crystals are stubby prisms, often pink to white. Some potassium feldspars, such as the one shown to the left have a streaky appearance (see closeup) called perthitic texture.

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