feldspaatin

Feldspaatin is a group of rock-forming tectosilicate minerals that together make up a large portion of the Earth’s crust. They are aluminosilicates with a framework of SiO4 and AlO4 tetrahedra, balanced by potassium, sodium, or calcium cations. Feldsats occur mainly in three chemical systems: alkali feldspars (potassium-rich) such as orthoclase, microcline and sanidine; and plagioclase feldspars, which form a continuous solid solution from albite to anorthite. The wide range of feldspar compositions is a defining feature of many rocks.

In natural rocks, feldspaatin minerals crystallize from magmas and also form by metamorphic recrystallization. They are common in granitic and other felsic rocks and appear as detrital grains in sedimentary rocks. Plagioclase-rich rocks feature albite and calcium-rich members in mafic compositions; alkali feldspars are typical of felsic rocks. A characteristic texture in potassium feldspar is perthite, formed by exsolution of intergrown sodium- and potassium-rich components, which can create a ribbon-like appearance.

Physical properties of feldspaatin include a Mohs hardness around 6, two cleavages at near 90 degrees, and a vitreous luster. Colors range from colorless to white, pink, gray, or brown; some varieties, such as labradorite, show iridescent internal flashes due to light interference within exsolution lamellae.

Uses and significance: feldspaatin is a major industrial mineral. Alkali and plagioclase feldspars are used in ceramics and glassmaking, as well as fillers and extenders. Potassium feldspar is a key source of alumina and potassium for manufacturing. Feldspar grains are also common detrital constituents in sedimentary rocks. In geochronology, potassium-bearing feldspars are used in K–Ar and Ar–Ar dating methods to determine geological ages.