Anorthite

specimen number:
2292362

location:
Antsohamamy quarry, Atsimo-Andrefana, Madagascar

description:
An attractive polished sphere of anorthite, this is the variety often called labradorite. This exhibits a great play of colors.

Labradorite is a calcium-rich plagioclase feldspar mineral, historically discovered in 1770 on Paul's Island near Nain, Labrador, Canada. Geologically, it crystallizes in mafic igneous rocks like basalt and anorthosite, containing an anorthite component of 50 to 70 percent. Its characteristic play of colors, called labradorescence, is caused by lamellar exsolution that occurs during slow cooling deep within the crust. This cooling process separates the mineral into microscopic, alternating layers of sodium-rich and calcium-rich feldspar. When light strikes these parallel layers, it undergoes optical interference and diffraction, reflecting specific wavelengths of light to produce metallic flashes of blue, green, and gold.

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