igneous
Labradorite-bearing anorthosite
Anorthosite, chiefly plagioclase feldspar (labradorite; approximately (Ca,Na)(Al,Si)₄O₈)
AI-generated identification · may be incorrectDark gray, coarse-grained, with blue-gray iridescent labradorescence; vitreous to pearly luster and feldspar cleavage. Hardness is about 6–6.5 Mohs; individual grains are crystalline, commonly with twinning, and specific gravity is about 2.65–2.75.
Identified More igneous →
Explore Labradorite-bearing anorthosite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray, coarse-grained, with blue-gray iridescent labradorescence; vitreous to pearly luster and feldspar cleavage. Hardness is about 6–6.5 Mohs; individual grains are crystalline, commonly with twinning, and specific gravity is about 2.65–2.75.
Formation & geological history
Formed when plagioclase-rich magma crystallized slowly in a deep igneous body, commonly during Precambrian crustal formation. The specimen appears tumbled or naturally smoothed, so texture and flashes are more diagnostic than its surface shape.
Uses & applications
Used as an ornamental stone, cabochon, carvings, countertops, and decorative aggregate; attractive material has modest lapidary value.
Geological facts
Labradorescence results from light interference within compositionally layered plagioclase crystals, not from surface coating. True anorthosite is overwhelmingly plagioclase, unlike many dark rocks sold commercially as “labradorite.”
Field identification & locations
Common sources include Labrador, Canada; Madagascar; Finland; Norway; and Ukraine. Identify it by gray-black plagioclase with blue, green, or gold flashes that change with viewing angle, plus feldspar cleavage and hardness near 6.
