Labradorite

Labradorite Sunstone Locality: Oregon © minclassics
Chemical Formula: (Ca,Na)[Al(Al,Si)Si2O8]
Locality: Labrador peninsula, Canada.
Name Origin: Named after its locality.Labradorite ((Ca,Na)[Al(Al,Si)Si2O8]), 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 2.68 to 2.72. The streak is white, like most silicates. The refractive index ranges from 1.559 to 1.573. 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.

Occurrence

The geological type area for labradorite is Paul’s Island near the town of Nain in Labrador, Canada. It has also been reported in Norway and various other locations worldwide.

Labradorite occurs in mafic igneous rocks and is the feldspar variety most common in basalt and gabbro. The uncommon anorthosite bodies are composed almost entirely of labradorite. It also is found in metamorphic amphibolites and as a detrital component of some sediments. Common mineral associates in igneous rocks include olivine, pyroxenes, amphiboles and magnetite.

History

Discovery date: 1780
Town of Origin : ILE DE PAUL, LABRADOR, NEWFOUNDLAND
Country of Origin : CANADA

Optical properties

Optical and misc. Properties : Translucent to transparent
Refractive Index: from 1,55 to 1,57
Axial angle 2V: 78-87°

Physical Properties

Cleavage: {001} Perfect, {010} Good, {110} Distinct
Color: Colorless, Gray, Gray white, White, Light green.
Density: 2.68 – 2.71, Average = 2.69
Diaphaneity: Translucent to transparent
Fracture: Uneven – Flat surfaces (not cleavage) fractured in an uneven pattern.
Hardness: 7 – Quartz
Luminescence: Non-fluorescent.
Luster: Vitreous (Glassy)
Streak: white

Photos :

Labradorite Mexico Thumbnail, 21.2 x 16.5 mm ; 19.90 carats © irocks
Anorthite (Var: Labradorite) Locality: Nain Complex, Labrador, Newfoundland and Labrador, Canada Dimensions: 9 cm x 4.5 cm x 1.5 cm Photo Copyright © 2000-2003 by John H. Betts
Photo Copyright © R.Weller/Cochise College.
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