Labradorite

Labradorite ((Ca,Na)(Al,Si)4O8), a feldspar mineral, is an intermediate to calcic member of the plagioclase series. It is usually defined as having "%An" (anorthite) between 50 and 70. The specific gravity ranges from 2.71 to 2.74. The streak is white, like most silicates. The refractive index ranges from 1.555 to 1.575. Twinning is common. As with all plagioclase members the crystal system is triclinic and three directions of cleavage are present two of which form nearly right angle prisms. It occurs as clear, white to gray, blocky to lath shaped grains in common mafic igneous rocks such as basalt and gabbro, as well as in anorthosites.

The geological type area for labradorite is Paul's Island near the town of Nain in Labrador, Canada. It occurs in large crystal masses in anorthosite and shows an iridescence or "play of colors". The iridescence is the result of light refracting within lamellar intergrowths resulting from phase exsolution on cooling in the Boggild miscibility gap, An48-An58.

Gemstone varieties of labradorite exhibiting a high degree of iridescence are called spectrolite; moonstone and sunstone are also commonly used terms, and high-quality samples with good iridescent qualities are desired for jewelry.

References

* Hurlbut, Cornelius S.; Klein, Cornelis, 1985, "Manual of Mineralogy", 20th ed., Wiley, ISBN 0-471-80580-7
* [http://webmineral.com/data/Labradorite.shtml Webmineral data]
* [http://www.galleries.com/minerals/silicate/labrador/labrador.htm Mineral galleries]
* [http://www.mindat.org/min-2308.html Mindat]


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  • Labradorite — Lab ra*dor ite, n. (Min.) A kind of feldspar commonly showing a beautiful play of colors, and hence much used for ornamental purposes. The finest specimens come from Labrador. See {Feldspar}. [1913 Webster] …   The Collaborative International Dictionary of English

  • labradorite — s. f. [Mineralogia] Ver lavradorite.   ♦ Grafia no Brasil: labradorita …   Dicionário da Língua Portuguesa

  • labradorite — [lab′rə dôr īt΄, lab΄rə dôr′īt΄] n. [after LABRADOR2, where specimens have been found] a variety of plagioclase with dark, iridescent colors …   English World dictionary

  • labradorite — labradoritic /lab reuh daw rit ik/, adj. /lab reuh daw ruyt , lab reuh dawr uyt/, n. a feldspar mineral of the plagioclase group, often characterized by a brilliant change of colors, with blue and green most common. [1805 15; named after LABRADOR …   Universalium

  • labradorite — labradoras statusas T sritis geologija ir mineralogija apibrėžtis Albito ir anortito izomorfinis mišinys, plagioklazas. atitikmenys: angl. labradorite rus. лабрадор …   Chemijos terminų aiškinamasis žodynas

  • labradorite — noun Etymology: Labrador Peninsula, Canada Date: 1814 an iridescent feldspar used especially in jewelry …   New Collegiate Dictionary

  • labradorite — noun A plagioclase feldspar, the fourth member of the Albite Anorthite solid solution series. Often very coarsely crystalline, it is used as a decorative stone for carvings and building façades. Crystal surfaces often show a bluish reflection… …   Wiktionary

  • labradorite — (la bra do ri t ) s. m. Terme de minéralogie. Feldspath à reflets opalins qu on trouve sur la côte du Labrador, et dont on fait des tables, des vases, etc.    On dit aussi labrador …   Dictionnaire de la Langue Française d'Émile Littré


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