This large star sapphire from Sri Lanka exhibits a rare 12-rayed star, probably caused by two sets of mineral inclusions oriented at 30° from each other. 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." Needlelike crystals of the mineral rutile inside the sapphire crystal that are aligned in three directions, intersecting at120°, form a 6-rayed star. Asterism is caused by light reflecting off of parallel bundles of tiny hollow tubes or fibrous crystals of another mineral inside the gemstone. ![]() ![]() It is an interesting member of the gem kingdom because it displays an optical phenomenon called asterism. Star sapphire is considered a phenomenal stone. ![]() This platinum ring has a round cabochon star sapphire as the centerpiece, accented with round brilliant cut diamonds set in "leaf-like" prongs, and baguette cut diamonds fanned on the sides of the shank.
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