A common rock-forming mineral occurring typically as white or pink crystals. It is a potassium-rich alkali feldspar and is used in ceramics and glass-making.
- Feldspars are added as orthoclase in order to reduce the devitrification of the glass.
- Of these, alkali feldspar, particularly orthoclase, is the most common.
- Associated minerals are white orthoclase, milky quartz, and muscovite.
Mid 19th century: from ortho- 'straight' + Greek klasis 'breaking' (because of the characteristic two cleavages at right angles).
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