Felsparteja

Felsparteja is a term used in geology to denote the feldspar group of rock‑forming silicate minerals. The word reflects a cross‑lingual adaptation of the common term feldspar and is encountered in several European language contexts. In this usage, felsparteja comprises the two main feldspar subgroups: plagioclase (a calcium–sodium feldspar series from anorthite to albite) and alkali feldspar (including orthoclase, microcline and sanidine). Both subgroups share a tectosilicate framework and vary mainly in chemical composition, with alkali feldspars richer in potassium and plagioclase richer in sodium and calcium.

Felsparteja minerals typically crystallize in monoclinic or triclinic systems. They have a Mohs hardness around 6 and exhibit two directions of cleavage at nearly right angles. Color ranges from white and gray to pink, green, or brown, often giving granite and other felsic rocks their characteristic appearance. Weathering of felsparteja can produce clay minerals such as illite or kaolinite and release alkalis into soils.

Geologically, felsparteja is among the most abundant mineral groups in Earth's crust, dominating much of granitic and other felsic rocks. Plagioclase is especially common in basaltic andesitic rocks, whereas alkali feldspar is prevalent in granitic compositions. The minerals also have important industrial uses, notably in glass and ceramic production, and in geochronology through potassium–argon dating in alkali feldspar samples.

Overall, felsparteja represents a broadly defined, essential mineral group whose precise classification is determined by chemical composition and crystal structure rather than by rock type alone.