labradorite

Labradorite is a plagioclase feldspar, a rock-forming mineral in the plagioclase series, with a chemical composition between albite (NaAlSi3O8) and anorthite (CaAl2Si2O8). It is best known for labradorescence, the iridescent colors that appear as light is reflected from lamellae inside the crystal.

The name derives from Labrador, Canada, where it was first described in the late 18th century. Higher-grade material from Finland is marketed as spectrolite. Labradorite occurs in igneous rocks such as basalt, gabbro, and anorthosite, and can also form in metamorphic environments.

In hand specimen the mineral ranges from gray to dark body color with vivid iridescent flashes of blue, green, yellow, or orange, depending on orientation and lighting. It has two cleavage directions at about 90 degrees, a Mohs hardness of about 6–6.5, and is typically translucent to opaque. The optical effect is caused by light interference within layered structures of the crystal.

Labradorite is used as a gemstone and decorative stone. It is commonly cut en cabochon to display its play of color and is also carved for ornamental objects. The term labradorescence describes the iridescent effect, while spectrolite refers to particularly vivid material from Finland.