Quartz and micas are typically associated minerals. Orthoclase is a common constituent of most granites and other felsic igneous rocks and often forms huge crystals and masses in pegmatite. [6], The largest documented single crystal of orthoclase was found in the Ural mountains in Russia. Orthoclase is one of the ten defining minerals of the Mohs scale of mineral hardness, on which it is listed as having a hardness of 6. admin Distinguishing orthoclase from its polymorphs, microcline and sanidine, can be very difficult without X-ray or opti-cal data. It can be difficult to see cleavage in thin section due to orthoclase's low relief. I certainly love this website. The common feldspar of granites, granite pegmatites, and syenites. The gemstone commonly called rainbow moonstone is more properly a colorless form of labradorite and can be distinguished from "true" moonstone by its greater transparency and play of color, although their value and durability do not greatly differ. Your email address will not be published. Required fields are marked *. Name Origin: From the Greek orthos - "right" and kalo -" I cleave" in allusion to the mineral's right angle of good cleavage. Science & Origin of OrthoclaseOrthoclase, also known as K-spar and K-feldspar, is a common potassium feldspar mineral that crystallizes in the form of masses, small prismatic shards, elongated crystals, and thin plate-like layers. Orthoclase, or orthoclase feldspar (endmember formula KAlSi3O8), is an important tectosilicate mineral which forms igneous rock. The resulting intergrowth of the two feldspars is called perthite. Color : white, pink, turbid. Orthoclase Meanings, Zodiacs, Planets, Elements, Colors, Chakras, and more. The name was changed in 1823 to orthoklas by Johann Friedrich August Breithaupt. Several other related minerals are known: Adularia is a colorless, transparent form of K-feldspar that forms prismatic crystals. Typically displays Carlsbad twinning. Optical Properties : In thin section, orthoclase has low birefringence, moderate relief, and resemblance to quartz. Orthoclase KAlSi3O8 °c 2001 Mineral Data Publishing, version 1.2 Crystal Data: Monoclinic. Cleavage/Fracture : 90° cleavage angle; perfect, Luster/Transparency : pearly, vitreous/translucent. It is a raw material used in the production of glass, ceramic tile, porcelain, dinnerware, bathroom fixtures, and other ceramics. It is a type of potassium feldspar, also known as K-feldspar.The gem known as moonstone (see below) is largely composed of orthoclase. EN; DE; FR; ES; Запомнить сайт; Словарь на свой сайт Cleavage/Fracture : 90° cleavage angle; perfect (001), good (010), poor {110}/uneven. Luster/Transparency : pearly, vitreous/translucent. In gemology, their luster is called adularescence and is typically described as creamy or silvery white with a "billowy" quality. Hand Specimen identification: Cleavage, hardness, luster, and association help identify anorthite, but it can be …, Your email address will not be published. [5] The optical effect of adularescence in moonstone is typically due to adularia. The lower-temperature polymorph of KAlSi3O8 is microcline. Together with their non-metallic luster and typically opaque character, these properties will usually distinguish feldspars from other common non-metallic minerals. Optical Properties : In thin section, orthoclase has low birefringence, moderate relief, and resemblance to quartz. However, it has negative relief, is biaxial, and is often clouded by fine-grained alteration. Alternate names are alkali feldspar, potassium feldspar an K-feldspar.The gem kent as muinstane is lairgely componed o orthoclase. K+ ions occupy available holes between the tetrahedra. Association with other fel-sic minerals also helps identification. It is sometimes confused with calcite or corundum but can be distinguished by its hardness. 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.