Sample in syenite
Sample in alkali granite
Sample in rhyolite porphyry
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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 (for instance grains on the left side of this specimen). The third direction fractures, however, and has an irregular, broken appearance (grain toward upper right). The surface is typically opaque, that is, light does not penetrate below the surface so the specimen almost looks painted. The clear, glassy, slightly gray minerals in this specimen is quartz.
In felsic igneous rocks orthoclase is common and may sometimes, when white, be confused with Na plagioclase. Pink orthoclase is distincive.
Note that there is a fair amount of quartz in this specimen (the clear, glassy grains in the rock).