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The geological type area for labradorite is Paul's Island near the town of Nain in Labrador, Canada. It occurs in large crystal masses in anorthosite and shows an iridescence or play of colors. The iridescence is the result of light refracting within perthitic lamellar intergrowths resulting from phase exsolution on cooling.
Gemstone varieties of labradorite exhibiting a high degree of iridescence are called spectrolite, moonstone and sunstone, and high-quality samples with good iridescent qualities are desired for jewelry.