mineralsfeldspars

Mineralsfeldspars, commonly referred to as feldspars, comprise the largest group of continental crust minerals. They are tectosilicates with a framework of linked SiO4 and AlO4 tetrahedra, in which charge balance is achieved by alkali metal ions (potassium, sodium) or calcium occupying positions in the crystal structure. Feldspars are divided into two main subgroups: alkali feldspars and plagioclase feldspars. Alkali feldspars include potassium varieties such as orthoclase, microcline, and sanidine, with general formula KAlSi3O8. Plagioclase feldspars form a continuous solid-solution series from albite (NaAlSi3O8) to anorthite (CaAl2Si2O8), with intermediate members such as oligoclase and andesine.

Feldspars occur in igneous rocks, particularly granites, granodiorites, and rhyolites, and are also common in metamorphic rocks like gneiss and schist, as well as in sedimentary units formed through weathering and cementation. They typically display two good cleavage directions at about 90 degrees and have a hardness around 6 on the Mohs scale. Color ranges from white to pink, grey, or colorless, with a vitreous to pearly luster. Albite and some plagioclase varieties can exhibit characteristic striations. Potassium feldspar may show exsolution textures and microcline often forms a mosaic or twinned appearance.

Industrially, feldspars are important as raw materials in glassmaking and ceramic production, acting as fluxes and sources of aluminum and silica. They weather to clay minerals and other alteration products, playing a major role in soil formation and geochemical cycles.