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The minerals in the feldspar family make up more than half of the Earth's crust. Occasionally these common minerals form crystals that shimmer like the light of the moon or a rainbow on a soap bubble. Called iridescence, this phenomenon is caused by light scattering, or diffracting, off closely spaced layers in the feldspar crystals. The gems cut from these iridescent crystals are called moonstones, sunstones, and labradorite. Sunstones exhibit a reddish to golden schiller, resulting from light reflecting off numerous tiny copper or hematite (iron oxide) flakes scattered within the stones. The golden sheen flashing off of this sunstone from Norway is due to the hematite inclusions.

Image Number: 95-40453
Catalog Number: G3273


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Smithsonian National Museum of Natural History Department of Mineral Sciences website Credits