Dictionary of Human Evolution and Biology

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Group of crystalline minerals consisting of silicates of aluminum and smaller amounts of sodium, potassium, barium and/or calcium; decomposition of feldspar produces clays. Stone tools are often made of this material, but feldspar possesses an internal crystal face that produces a preferential cleavage plane and that makes it difficult or impossible to control fracture and to produce a sharp-edged tool. Feldspar is important in the manufacture of porcelain and glazes. Aka felspar, felstone.