orthoclase

/awr"theuh klays', -klayz'/, n.
a common white or pink mineral of the feldspar group, KAlSi3O8, having two good cleavages at right angles, and found in silica-rich igneous rocks: used in the manufacture of porcelain.
[1840-50; ORTHO- + -clase < Gk klásis cleavage, breaking]

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Common alkali feldspar mineral, potassium aluminosilicate (KAlSi3O8), that usually occurs as variously coloured grains in granite.

Orthoclase is used in the manufacture of glass and ceramics; occasionally, transparent crystals are cut as gems. It is primarily important as a rock-forming mineral, however, and is abundant in igneous rocks, pegmatites, and gneisses. The feldspar minerals consist of sodium, potassium, and calcium aluminosilicates, and any feldspar may be chemically classed by the percentage of each of these three pure compounds, called end-members. Orthoclase is the potassium-bearing end-member of the system. Microcline is a lower temperature structural form of the same chemical composition as orthoclase.

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 common alkali feldspar mineral, a potassium aluminosilicate (KAlSi3O8); it usually occurs as variously coloured, frequently twinned crystals in granite. Orthoclase is used in the manufacture of glass and ceramics; occasionally, transparent crystals are cut as gems. Orthoclase is primarily important as a rock-forming mineral, however, and is abundant in alkali and acidic igneous rocks, in pegmatites, and in gneisses. For detailed physical properties, see feldspar (table).

      The feldspar minerals are mixtures of sodium, potassium, and calcium aluminosilicates, and any feldspar may be classed by its percentage of each of these three pure compounds, called end-members. Orthoclase is the potassium-bearing end-member of the system; its symbol is Or.

      Orthoclase and the sodium-bearing end-member of the system, albite (sodium aluminosilicate; NaAlSi3O8), form the alkali feldspars, a series in which sodium-bearing and potassium-bearing species intermingle; thus, there is a continuous chemical variation between the two end-members. Because the intermediate members, called orthoclase–microperthites, cannot blend homogeneously, they take the form of intergrowths of microscopic but distinct crystals of the sodium and potassium end-members.

      Orthoclase has an intermediate degree of ordering of the aluminum and silicon atoms in its aluminosilicate crystal framework, falling between the fully ordered arrangement of microcline and the random arrangement of high-sanidine.

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Universalium. 2010.

Synonyms:

Look at other dictionaries:

  • Orthoclase — General Category Silicate mineral Chemical formula KAlSi3O8 …   Wikipedia

  • Orthoclase — Or tho*clase, n. [Ortho + Gr. ? to break.] (Min.) Common or potash feldspar crystallizing in the monoclinic system and having two cleavages at right angles to each other. See {Feldspar}. [1913 Webster] …   The Collaborative International Dictionary of English

  • orthoclase — [ôr′thō klās΄, ôr′thōklāz΄; ôr′thəklās΄, ôr′thəklāz΄] n. [Ger orthoklas < Gr orthos (see ORTHO ) + klasis, fracture (< klan, to break: see CLASTIC), because of the 90° cleavage] a monoclinic feldspar, KAlSi3O8, that is dimorphic with… …   English World dictionary

  • Orthoclase — Orthose Orthose Catégorie IX : silicates Orthose et quartz Généra …   Wikipédia en Français

  • orthoclase — noun Potassium aluminum silicate, KAlSiO, a common feldspar of igneous, plutonic, and metamorphic rocks. Orthoclase is the main feldspar of pegmatite occurrences, where it is most commonly flesh colored. Orthoclase is used in the ceramic and …   Wiktionary

  • orthoclase — ortoklazas statusas T sritis chemija apibrėžtis Mineralas. formulė K[AlSi₃O₈] atitikmenys: angl. orthoclase rus. ортоклаз …   Chemijos terminų aiškinamasis žodynas

  • orthoclase — noun Etymology: German Orthoklas, from orth + Greek klasis breaking, from klan to break more at clast Date: 1849 a monoclinic mineral of the feldspar group consisting of a silicate of potassium and aluminum …   New Collegiate Dictionary

  • orthoclase — [ ɔ:θəkleɪz] noun a potassium rich mineral of the feldspar group, typically white or pink. Origin C19: from ortho + Gk klasis breaking (because of the characteristic two cleavages at right angles) …   English new terms dictionary

  • orthoclase — n. Potash felspar, orthose, prismatic felspar, felspar …   New dictionary of synonyms

  • orthoclase — or·tho·clase …   English syllables

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