An alternative spelling of feldspar, one of the most abundant minerals in Earth's crust, commonly used in ceramics and glass.
From German 'Feldspat,' where 'Feld' means field (referring to common occurrence in fields) and 'Spat' derives from 'spathus' (meaning spar or cleavable mineral). This older English spelling reflects direct borrowing from German mineralogy terminology.
Feldspar—or felspar in older texts—is so common that it literally makes up about 60% of Earth's continental crust, yet most people have never heard of it despite wearing glass made from it and using ceramics containing it daily.
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