feldspätmineralen

Feldspätmineralen (feldspar minerals) are the most abundant group of minerals in the Earth's crust, constituting roughly 60 percent of its mass. They are tectosilicates with a framework of linked silicon-oxygen tetrahedra that forms a rigid three-dimensional structure. Feldspars occur in two major subgroups: alkali feldspar and plagioclase feldspar.

Alkali feldspar includes minerals such as orthoclase, microcline, and sanidine, with a general composition near KAlSi3O8 and varying amounts of Na. Plagioclase feldspars form a continuous solid solution between albite NaAlSi3O8 and anorthite CaAl2Si2O8, with the precise makeup dictated by geological history. Plagioclase often shows characteristic striations on cleavage surfaces and two cleavage directions that are close to 90 degrees.

Physically, feldspars typically exhibit a vitreous luster, range from colorless to pinkish or white (with impurities causing variations), and have a Mohs hardness around 6. They commonly occur as the dominant minerals in igneous rocks such as granites, granodiorites, and rhyolites, and they are also found in metamorphic rocks and as detrital grains in sedimentary rocks.

Geochemically and industrially, feldspars are important for dating and applications. They are used in glass and ceramics as silica-alumina sources and as flux agents; potassium feldspars enable K-Ar and Ar-Ar dating techniques. Weathering alters feldspars to clay minerals (e.g., kaolinite, illite), influencing soil formation and nutrient availability. Feldspar minerals thus play a central role in crustal geology, technology, and soil science.