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Smithsonian National Museum of Natural History

Fire Opal

Opal (var. fire opal) from Brazil
Photo by Ken Larsen. Click to zoom.
Catalog Number NMNH G11440-00
Locality Brazil
Weight 75.5 ct

Opal is a noncrystalline hydrated form of silica (silicon and oxygen), forming when an undisturbed space in a rock holds a clean solution of silica from which water is slowly removed over a period of thousands of years. Opals are described according to their transparency and body color. Fire opals are transparent to semi-transparent, resembling gelatin, with red, orange, or yellow body color, with or without play-of-color. Fire opal gets its name from its intense reddish-orange body color, which is caused by inclusions of iron oxides. Mexico has the most significant fire opal deposits in the world, but they are also mined commercially in Brazil. Brazilian fire opals range in color from pale yellow to light red and are transparent, sometimes with a slight clouding and most often without play-of-color. Opals are typically cut as cabochons or polished free-form. However, because of their transparency and vibrant color, fire opals are commonly faceted, as seen here in this triangular cut gem. This 75.50 carat intense yellowish-orange fire opal from Brazil was acquired with funds from the Tiffany & Co. Foundation endowment in 2012 and is the largest Brazilian fire opal in the National Gem Collection.


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