Crystallography : Monoclinic, a = 8.56, b = 12.99, c = 7.19, b = 116.01°, Z = 4; space group C 2/m; point group 2/m. Distinguishing orthoclase from its polymorphs, microcline and sanidine, can be very difficult without X-ray or opti-cal data. Cleavages intersect at 90°. [4] It was first described by Ermenegildo Pini in 1781. It is dis-tinguished from sanidine by 2V and from micro-cline by its lack of plaid twinning. Quartz and micas are typically associated minerals. Your email address will not be published. Optical Properties : In thin section, orthoclase has low birefringence, moderate relief, and resemblance to quartz. All of the feldspar minerals exhibit a blocky crystal habit, hardness greater than glass, and two directions of cleavage that meet at nearly right angles. feldspar group General Orthoclase Information : Chemical Formula: KAlSi3O8 : Composition: Molecular Weight = 278.33 gm Potassium 14.05 % K 16.92 % K 2 O: Aluminum 9.69 % Al 18.32 % Al 2 O 3: Silicon 30.27 % Si 64.76 % SiO 2: Oxygen 45.99 % O: 100.00 % 100.00 % = TOTAL OXIDE Adularia is a low temperature form of either microcline or orthoclase originally reported from the low temperature hydrothermal deposits in the Adula Alps of Switzerland. I certainly love this website. Most moonstones are translucent and white, although grey and peach-colored varieties also occur. Perthite is a form of K-feldspar contain-ing exsolved patches or lamellae of albitic feldspar (refer to Plate 6.7). Cleavage/Fracture : 90° cleavage angle; perfect, Luster/Transparency : pearly, vitreous/translucent. Baveno and manebach twins have also been reported in orthoclase. 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. The sense of Haüy's name was that the mineral was a feldspar, but he did not specify a type-locality, nor did Haüy give a chemical analysis. It is sometimes confused with calcite or corundum but can be distinguished by its hardness. Геофизика: ортоклаз. Name Origin: From the Greek orthos - "right" and kalo -" I cleave" in allusion to the mineral's right angle of good cleavage. Cleavage/Fracture : 90° cleavage angle; perfect (001), good (010), poor {110}/uneven. Hand Specimen identification: The luster, hardness, and color of orthoclase are similar to other feldspars, but (in contrast with pla-gioclase) orthoclase is frequently pink or flesh col-ored, has cleavage planes that meet at 90o, and does not show twin striations. Most orthoclase contains some Na replacing K; complete solid solution between. Cleavable, granular, massive. The gem known as moonstone (see below) is largely composed of orthoclase. Alternate names are alkali feldspar, potassium feldspar an K-feldspar.The gem kent as muinstane is lairgely componed o orthoclase. lelang barang bekas kantor: What's up, every time i used to check webpage posts here early in the morning, a... watches shop: Incredible points. It is a raw material used in the production of glass, ceramic tile, porcelain, dinnerware, bathroom fixtures, and other ceramics. Plate 1.5 is a color photo of twinned orthoclase crystals. It is also cut as a gemstone. Luster/Transparency : pearly, vitreous/translucent. In cavities in basalts; in high-grade metamorphic rocks and as a result of potassic hydrothermal alteration; also authigenic and detrital. Orthoclase is a common constituent of most granites and other felsic igneous rocks and often forms huge crystals and masses in pegmatite. dic.academic.ru RU. If it shows opalescence, we call it moonstone. An adularescent gem material known as moonstone is an intergrowth of orthoclase and albite. Structure and composition : The structure of orthoclase consists of a three-dimensional framework of SiO4 and AlO4 tetrahe-dra. Color : white, pink, turbid. Penetration twins and contact twins are common. Together with the other potassium feldspars, orthoclase is a common raw material for the manufacture of some glasses and some ceramics such as porcelain, and as a constituent of scouring powder. Orthoclase, or orthoclase feldspar (endmember formula KAlSi3O8), 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. [8], Tectosilicate mineral found in igneous rock, "Orthoclase: Orthoclase mineral information and data", "Adularia: Adularia mineral information and data", "Moonstone Value, Price, and Jewelry Information", http://www.nasa.gov/press/2014/june/nasa-s-mars-curiosity-rover-marks-first-martian-year-with-mission-successes, https://en.wikipedia.org/w/index.php?title=Orthoclase&oldid=968301947, Short description is different from Wikidata, Creative Commons Attribution-ShareAlike License, Colorless, greenish, greyish yellow, white, pink. This page was last edited on 18 July 2020, at 14:38. The common feldspar of granites, granite pegmatites, and syenites. The lower-temperature polymorph of KAlSi3O8 is microcline. In gemology, their luster is called adularescence and is typically described as creamy or silvery white with a "billowy" quality. [6], The largest documented single crystal of orthoclase was found in the Ural mountains in Russia. It measured ~10×10×0.4 m and weighed ~100 tons.[7]. 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. Typically, the pure potassium endmember of orthoclase forms a solid solution with albite, the sodium endmember (NaAlSi3O8), of plagioclase. Leave a comment The sense of Haüy's name was that the mineral was a feldspar, but he did not specify a type-locality, nor did Haüy give a chemical analysis. Some intergrowths of orthoclase and albite have an attractive pale luster and are called moonstone when used in jewellery. The name is from the Ancient Greek for "straight fracture," because its two cleavage planes are at right angles to each other. Typically displays Carlsbad twinning. Occurrence and associations : Orthoclase is common in many kinds of silicic ig-neous rocks, sediments such as arkoses, and a variety of metamorphic rocks. Point Group: 2=m: Crystals commonly short prismatic along [100] or [001], tabular on [010], to 20 cm. Orthoclase KAlSi3O8 °c 2001 Mineral Data Publishing, version 1.2 Crystal Data: Monoclinic. Several other related minerals are known: Adularia is a colorless, transparent form of K-feldspar that forms prismatic crystals.