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A feldspar mineral, pink, white, greenish with two directions of cleavage at 90 degrees. Cleavages are well developed and commonly seen in specimens in rocks. The third direction fractures, however, and has an irregular, broken appearance. The surface is typically opaque, that is, light does not penetrate below the surface so the specimen almost looks painted.
Feldspar crystal structure is complex but consists of rings of four tetrahedra (resulting in the 90o cleavage), strung into warped chains, held together ionically by metallic cations. The specific cations determine the particular feldspar obtained (see link).
In felsic igneous rocks orthoclase is common and may sometimes, when white, be confused with Na plagioclase. Pink orthoclase distinctive.