- Orthoclase (endmember formula KAlSi3O8), an important tectosilicate mineral that forms igneous rock
- Microcline, chemically the same as orthoclase, but with a different crystalline structure
- Sanidine, the high-temperature form of potassium feldspar (K,Na)(Si,Al)4O8
- Adularia, a more ordered low-temperature variety of orthoclase or partially disordered microcline
- Amazonite (sometimes called "Amazon stone"), a green variety of microcline
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