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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 feldspar group of minerals consists of tectosilicates, silicate minerals in which silicon ions are linked by shared oxygen ions to form a three-dimensional network. Compositions of major elements in common feldspars can be expressed in terms of three endmembers: potassium feldspar (K-spar) endmember K Al Si 3 O 8 [14] albite endmember ...
Microcline may be chemically the same as monoclinic orthoclase, but because it belongs to the triclinic crystal system, the prism angle is slightly less than right angles; hence the name "microcline" from the Greek "small slope". It is a fully ordered triclinic modification of potassium feldspar and is dimorphous with orthoclase. Microcline is ...
Perthitic textures: antiperthite (1), perthite (2), and mesoperthite (3) Perthite or perthitic texture is used to describe an intergrowth of two feldspars: a host grain of potassium-rich alkali feldspar (near K-feldspar, KAlSi 3 O 8, in composition) includes exsolved lamellae or irregular intergrowths of sodic alkali feldspar (near albite, NaAlSi 3 O 8, in composition).
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.
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 feldspar is usually orthoclase, but can also be albite, oligoclase or microcline. In at least some instances, quartz is so disposed that the two minerals have a definite relation between their crystallographic axes.
According to the Goldich dissolution series, anorthite, a plagioclase feldspar, should weather quickly, with a lifetime of 10 5.62 years quantified by Kowalski and Rimstidt. [1] [5] Conversely, the lifetime of K-feldspar should be much longer, at 10 8.53 years based again on Kowalski and Rimstidt’s work. However, White and Brantley’s ...