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Detail of labradorite feldspar displaying typical labradorescence.

Labradorite

Credit: Gregory Phillips

Labradorite ((Ca,Na)(Al,Si)₄O₈) is a feldspar mineral of the plagioclase series. Here, a piece of labradorite displays a typical iridescence, termed labradorescence, caused by the refraction of light within the crystal. Gemstone varieties of labradorite exhibit high degrees of iridescence, and are called spectrolites, moonstones or sunstones.