The sapphires in this group vary in color from deep blue to gold, and they come from widely separated localities. The scatter of small multicolored stones came from Montana, and the magnificent 93-carat golden sapphire, encircled by the gold bracelet, came from Burma. (Slightly less than half actual size.)
There are some notable exceptions to the generally oriental occurrence of corundum. Some good-quality ruby has been found in North Carolina, and sapphire of many colors has come from Montana.
During the formation of a corundum crystal, extremely small needle-like inclusions of rutile sometimes occur in the hexagonal pattern of the host crystal. When such inclusions are arranged in this way by nature, they cause, in properly cut stones, internal reflections that produce the optical phenomenon known as asterism. The effect is that of a 6-rayed star, and the gems in which asterism occurs are known as star sapphires and star rubies. Asterism is rarer in ruby.
The Star of Asia, weighing 330 carats, is one of the finest star sapphires in the world. It is of a clear, deep blue color and has a strong, sharply defined, 6-rayed star. (Actual size.)
Cutting a star stone requires careful attention to the directions in which the cuts are to be made. Failure to align the stone properly with the axis of the crystal will produce a stone with an off-center, crooked, or dim star, or may even eliminate the star completely.
CRYSTAL AXIS POSITION STONE MUST TAKE TO SHOW STAR OTHER STAR STONES MAY BE CUT, BUT MUST BE IN THE SAME POSITION WITHIN THE CRYSTAL ROUGH SAPPHIRE CRYSTAL CRYSTAL AXIS
Since corundum is easily manufactured, synthetic ruby and sapphire are used extensively in jewelry. The synthetic stones can be distinguished from natural stones by microscopic examination of the kinds of inclusions and internal defects.
VARIETIES Ruby: Red. Sapphire: Blue, yellow, pink, green, colorless, and any color except red. Star sapphire: Colored as sapphire and showing asterism. Star ruby: Red and showing asterism.