Orthoklase

Orthoclase is a common tectosilicate mineral of the feldspar group. Its chemical formula is KAlSi3O8, representing potassium aluminum silicate. It is one of the most abundant minerals in the Earth's crust, found in various igneous, metamorphic, and sedimentary rocks. Orthoclase is typically colorless, white, or gray, though impurities can give it pink, yellow, or greenish hues. It crystallizes in the monoclinic system, often forming prismatic or tabular crystals. A characteristic feature of orthoclase is its perfect cleavage in two directions, which intersect at nearly 90 degrees. It has a hardness of 6 on the Mohs scale, making it relatively hard but susceptible to scratching by harder minerals. Orthoclase is a primary constituent of granite and is also found in syenites, gneisses, and some sandstones. It weathers relatively easily, transforming into clay minerals such as kaolinite. Varieties of orthoclase include adularia, which forms clear, often tabular crystals found in alpine veins, and moonstone, a gem variety known for its adularescence, a pearly, bluish sheen. Orthoclase plays a significant role in rock formation and weathering processes and is sometimes used in the ceramics industry and as a minor source of potash.