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Labradorite
Chemical Formula	(Ca,Na)(Al,Si)4O8, where Ca/(Ca + Na) (% anorthite) is between 50%–70%
Species	Silicates
Crystal System	Triclinic
Mohs Scale	6
Specific Gravity	2.68-2.72
Color	Gray, brown, greenish, blue, yellow, colorless
Streak	white
Luster	Sub-Vitreous
Refractive Index	n = 1.554 - 1.563 n = 1.559 - 1.568 n = 1.562 - 1.573
Diaphaneity	Translucent to transparent
Cleavage	Perfect
Fracture	Uneven to conchoidal
Crystal Habit：Crystals typically thin and tabular, rhombic in cross section, striated; massive

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 2.68 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.

Labradorescence

It occurs in large crystal masses in anorthosite and shows a play of colors called labradorescence. The labradorescence, or schiller effect, is the result of light refracting within lamellar intergrowths resulting from phase exsolution on cooling in the Boggild miscibility gap, An₄₈-An₅₈.^{[further explanation needed]}

Gemstone varieties of labradorite exhibiting a high degree of labradorescence are called spectrolite.

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