Feldspar Group

Feldspar is the name of a group of aluminium silicate minerals, and is collectively the most common mineral group found on the surface of the Earth. The major rock-forming minerals in the feldspar group include albite, anorthite, orthoclase and microcline. In petrology, the group is split into two major subgroups: Alkali feldspar - feldspar minerals poor in calcium, and mostly rich in potassium. At high temperature, the alkali feldspars form a series from sanidine to high albite; the series is incomplete at low temperature. Some workers include barium feldspars (celsian and hyalophane) and probably the rubidium feldspar rubicline, as alkali feldspars. Plagioclase - the albite to anorthite series. Feldspars may contain very minor amounts of OH groups, considered as defects (e.g., Yang et al., 2015).