labradorite
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labradorite
(lăb`rədôrīt', lăbrədôr`īt), a variety of plagioclase feldsparfeldsparor felspar
, an abundant group of rock-forming minerals which constitute 60% of the earth's crust. Chemically the feldspars are silicates of aluminum, containing sodium, potassium, iron, calcium, or barium or combinations of these elements.
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Labradorite
(named for a deposit on Labrador), a mineral of the soda-lime feldspars—the plagioclases. It is an isomorphic mixture of soda feldspar (albite) with lime feldspar (anorthite). The mineral contains 50–70 percent anorthite. It crystallizes in the triclinic system; it is colorless, white, or gray and forms complex twins, often with an attractive blue-green and golden iridescence. Its hardness is 6 on the Mohs’ scale and its density is 2,680–2,720 kg/m3. Labradorite enters into the composition of many basic magmatic rocks, including gabbros, basalts, and diabases. Rocks consisting almost entirely of labradorite are called labradoritites.
labradorite
[′lab·rə‚dȯ‚rīt] (mineralogy)
A gray, blue, green, or brown plagioclase feldspar with composition ranging from Ab50 An50 to Ab30 An70, where Ab = NaAlSi3O8 and An = CaAl2Si2O8; in the course of formation when the natural material cools, the feldspar sometimes exhibits a variously colored luster. Also known as Labrador spar.