Description
Feldspar is the name for a group of rock-forming minerals that constitute an estimated 60% of the Earth's crust. They are aluminum tetrasilicates; silicates in which the silica tetrahedra are arranged in a three-dimensional pattern. The word feldspar is derived from the German words Feld and Spath, "a rock that contains no ore." There are three types of feldspar: potassium aluminum silicates, sodium aluminum silicates, and calcium aluminum silicates. Isomorphous mixtures of these three compounds also belong to the feldspar group. Feldspars are usually divided into: potassium feldspar series – (Na,K) feldspars; orthoclase; plagioclase series – (Na,Ca) feldspars; albite – anorthite. The two series form so-called solid solutions. Among the plagioclases, the intermediate feldspars are named according to their composition.
