labradorite

labradorite (lăbˈrədôrītˌ, lăbrədôrˈīt), a variety of plagioclase feldspar.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

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.

References in periodicals archive ?

Hellmann R, Penisson JM, Hervig RL, Thomassin JH, Abrioux MF (2003) An EFTEM/HRTEM high-resolution study of the near surface of labradorite feldspar altered at acid pH: evidence for interfacial dissolution-reprecipitation.

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Name 1 Carbuncle 2 K feldspar 3 Albite 4 Tektite 5 Magnetite 6 Demantoid 7 Oolitic hematite 8 Pink pyroxene 9 Idocrase 10 Black hematite 11 Biotite 12 Hornblende 13 Calcite 14 Labradorite 15 Magnesite 16 Rhodonite 17 Reniform hematite 18 Banded siliceous rocks 19 Diopside 20 Selenite 21 Alabaster 22 Anhydrite 23 Moonstone 24 Barite 25 Hypersthene Table 2: Emission lines for classification based on major elements from geological samples.

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The matrix has a poikiloophitic texture formed predominantly by plagioclase (labradorite, [An.sub.60-65], in some grains bytownite, [An.sub.70-75]) enclosed by elongated hypidiomorphic brownish augite crystals of 0.3-0.8 mm length and isometric grains of subordinated olivine and biotite; accessory phases are apatite and magnetite.

Geochemistry and [sup.40]Ar/[sup.39]Ar age of early carboniferous dolerite sills in the southern Baltic sea/Laanemere lounaosa Vara-Karboni doleriitsete sillide geokeemia ja [sup.40]Ar/[sup.39]Ar isotoopvanus

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Plagioclase phenocrysts (bytownite or labradorite; [An.sub.64-72]) have rims that are both similar to, and more sodic than, the calcic cores, with some solid solution variation within the cluster.

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On the other hand, feldspar from the central facies is classified as plagioclase, with compositions ranging from labradorite to anorthoclase ([An.sub.64-14] [Ab.sub.34-73] [Or.sub.01-12]; Table 1; Fig.

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Plagioclases in trachyandesites are characterized by andesine to labradorite composition (37 to 65% An, Table 1).

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