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Smithsonian National Museum of Natural History

Corundum (var. sapphire)

Photograph of an uncut sapphire crystal (171220) from the National Mineral Collection
Photo by Chip Clark. Click to zoom.
Catalog Number NMNH 171220-00
Locality Sri Lanka

Purchased in 1996.

Sapphire is a blue, yellow, orange, pink, purple, green or clear variety of the mineral corundum. Pure corundum is colorless, but tiny amounts of impurity trapped in the crystals as they grow result in a range of vivid colors. Iron and titanium are responsible for the deep blue color of sapphires. This 175.1ct sapphire crystal reveals the typical natural shape of corundum crystals. To obtain the deepest color, gems are oriented so that the top of the cut stone is perpendicular to the length of the crystal. If this corundum crystal was cut, the faceted gems would probably be pink or purple in color. Today, ninety percent of corundum is heat-treated to enhance its color.



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