Reference work entry
Feldspar gemstones are composed of gem-grade feldspar, which is a common mineral in the Earth’s crust. Its chemical composition is K, Na, Ca and Ae silicate. Feldspar is a large mineral group with many varieties. The main sub-groups are K-feldspar, plagioclase feldspar and barium feldspar, whereas K-feldspar and plagioclase feldspar are used as gemstones. Common feldspar gems include moonstone (belomorite), adularia, sanidinite, amazonite and sunstone (sandastras) (Fig. 2).
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