perthite

perthite
perthitic /peuhr thit"ik/, adj.perthitically, adv.
/perr"thuyt/, n. Mineral
a variety of feldspar containing irregular bands of albite in microcline.
[1832; named after Perth, Ontario, Canada; see -ITE1]

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      any member of a class of alkali feldspars in which tiny crystals of sodium-rich feldspar (albite; NaAlSi3O8) are intimately intergrown with, but distinct from, tiny crystals of potassium-rich feldspar (orthoclase or, less commonly, microcline; KAlSi3O8). Slow cooling of a homogeneous, molten mixture of sodium and potassium feldspar induces instabilities and results in the separation of tiny crystals of the two phases. In perthite, they sometimes may be seen by the unaided eye; in microperthite, however, they are distinguishable only microscopically, and in cryptoperthite the crystals are so small that the separation can be detected only by X-ray diffraction. Perthite was originally thought to be a single mineral, described at a locality near Perth, Ontario, from which its name is derived.

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Universalium. 2010.

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  • Perthite — is used to describe an intergrowth of two feldspars: a host grain of potassium rich alkali feldspar (near K feldspar, KAlSi3O8, in composition) includes exsolved lamellae or irregular intergrowths of sodic alkali feldspar (near albite, NaAlSi3O8 …   Wikipedia

  • Perthite — Perth ite, n. [So called from Perth, in canada.] (Min.) A kind of feldspar consisting of a laminated intertexture of albite and orthoclase, usually of different colors. {Per*thit ic}, a. [1913 Webster] …   The Collaborative International Dictionary of English

  • perthite — ● perthite nom féminin Cristal mixte de feldspath sodique et de feldspath potassique résultant de la démixtion à basse température d une phase cristalline sodipotassique, homogène à haute température …   Encyclopédie Universelle

  • perthite — noun A laminated mixture of two feldspars of different colours …   Wiktionary

  • perthite — perth·ite …   English syllables

  • Perthite — /ˈpɜθaɪt/ (say perthuyt) noun 1. someone who was born in Perth, WA, or who has come to regard it as his or her home. –adjective 2. of or relating to the city of Perth, WA …  

  • perthite — …   Useful english dictionary

  • Perthitic — Perthite Perth ite, n. [So called from Perth, in canada.] (Min.) A kind of feldspar consisting of a laminated intertexture of albite and orthoclase, usually of different colors. {Per*thit ic}, a. [1913 Webster] …   The Collaborative International Dictionary of English

  • feldspar — /feld spahr , fel /, n. any of a group of minerals, principally aluminosilicates of potassium, sodium, and calcium, characterized by two cleavages at nearly right angles: one of the most important constituents of igneous rocks. Also, felspar.… …   Universalium

  • Feldspar — is the name of a group of rock forming minerals which make up as much as 60% of the Earth s crust.Feldspar. [http://www.ima na.org/about industrial minerals/feldspar.asp What is Feldspar?] Industrial Minerals Association. Retrieved on July 18… …   Wikipedia

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