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Star Sapphire Necklace

Photograph of a star sapphire necklace (NMNH G8887) from the National Gem Collection
Photo by Chip Clark. Click to zoom.
Catalog Number NMNH G8887-00
Locality Sri Lanka
Weight 60 ct

Added to the collection in 1981.This object was designed by Marcus & Co.

This Edwardian (1901-1915) platinum necklace designed by Marcus & Co. features a 60-carat sky blue star sapphire from Sri Lanka in a setting studded with 126 diamonds accented with bows. Star sapphire is considered a phenomenal stone. It is an interesting member of the gem kingdom because it displays an optical phenomenon called asterism. Asterism is light reflected off of parallel inclusions of microscopic tubes or crystals of another mineral inside the gemstone. When a stone is cut with a domed top and flat bottom, called a cabochon, the reflected light is focused into bright bands that form the “star.” In this case it is needlelike crystals of the mineral rutile inside the sapphire crystal that are aligned in three directions, intersecting (@120°) to form the 6-rayed star. Because of these inclusions, which form the phenomenon and make the gem less transparent, this quality of gem rough is cut en cabochon and would not be faceted. This beautiful necklace was donated to the Smithsonian in 1981 and is on exhibit at the National Museum of Natural History.


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