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Orthoclase, or orthoclase feldspar (endmember formula K Al Si 3 O 8), is an important tectosilicate mineral which forms igneous rock. The name is from the Ancient Greek for "straight fracture", because its two cleavage planes are at right angles to each other. It is a type of potassium feldspar, also known as K-feldspar.
The dominant green epidote in unakite rocks is the metasomatic alteration product of plagioclase feldspar, while the orthoclase and quartz crystals remain unaffected.
Feldspar is a common raw material used in glassmaking, ceramics, and to some extent as filler and an extender in paint, plastics, and rubber. In the US, about 66% of feldspar is consumed in glassmaking, including glass containers and glass fibre.
Potassium feldspar refers to a number of minerals in the feldspar group that contain large amounts of potassium in the crystal lattice. Orthoclase (endmember formula K Al Si 3 O 8), an important tectosilicate mineral that forms igneous rock; Microcline, chemically the same as orthoclase, but with a different crystalline structure
The most common moonstone is of the orthoclase feldspar mineral adularia, named for an early mining site near Mt. Adular in Switzerland, now the town of St. Gotthard. [1] [better source needed] A solid solution of the plagioclase feldspar oligoclase +/− the potassium feldspar orthoclase also produces moonstone specimens.
Phenocrysts of clear glassy rounded quartz and white orthoclase feldspar are set in a fine-grained matrix. Sample is just over 10 cm long Sample is just over 10 cm long Quartz-porphyry , in layman's terms, is a type of volcanic ( igneous ) rock containing large porphyritic crystals of quartz .
Orthoclase is a monoclinic polymorph stable at lower temperatures. At yet lower temperatures, microcline, a triclinic polymorph of potassium feldspar, is stable. Due to the high temperature and rapid quenching, sanidine can contain more sodium in its structure than the two polymorphs that equilibrated at lower temperatures.
Sunstone is a microcline or oligoclase feldspar, which when viewed from certain directions exhibits a spangled appearance. It has been found in Southern Norway, Sweden, various United States localities and on some beaches along the midcoast of South Australia.