A star sapphire is a gemstone composed of corundum, aluminum oxide, which displays asterism. This phenomenon arises from the presence in the gemstone of tiny strands of minerals that capture and reflect light in a star pattern. The star, which appears to move around as the position of the sapphire changes, usually has six rays, but 12-ray stars also sometimes occur. Star sapphires come in several colors, including blue, rose, smoky brown and translucent, which is especially prized. Linde star sapphires are synthetic gemstones that also exhibit asterism. Like the natural stones, they come in a variety of colors, though the stars in them do not move. Since their accidental creation, they have become very popular in gemstone jewelry.
The Brazilian Connection, an online retailer of gemstones and gemstone jewelry, conducted an interview with Jack Burdick, an inventor who worked for Linde Air Products Co. In 1947, Burdick and his colleagues were trying to create synthetic sapphires with consistent color throughout, a goal that had eluded chemists for decades. In the laboratory, Burdick and his team created sapphires with only titania in them. They heated the resulting gems for several days and then took them out of the furnace, only to learn that they were milky rather than clear.
SYNTHETIC STAR STONES PROPERTIES:
CHEMICAL COMPOSITION: ALO2
HARDNESS MOH'S: 9
SYNTHETIC STAR STONES:
1. STAR RUBY
2. STAR SAPPHIRE
3. TRANSPARENT STAR RUBY
A star sapphire is a type of sapphire that exhibits a star-like phenomenon known as asterism; red stones are known as "star rubies". Star sapphires contain intersecting needle-like inclusions following the underlying crystal structure that cause the appearance of a six-rayed "star"-shaped pattern when viewed with a single overhead light source. The inclusion is often the mineral rutile, a mineral composed primarily of titanium dioxide. The stones are cut en cabochon, typically with the center of the star near the top of the dome.
Occasionally, twelve-rayed stars are found, typically because two different sets of inclusions are found within the same stone, such as a combination of fine needles of rutile with small platelets of hematite; the first results in a whitish star and the second results in a golden-colored star. During crystallisation, the two types of inclusions become preferentially oriented in different directions within the crystal, thereby forming two six-rayed stars that are superimposed upon each other to form a twelve-rayed star. Misshapen stars or 12-rayed stars may also form as a result of twinning. The inclusions can alternatively produce a "cat's eye" effect if the 'face-up' direction of the cabochon's dome is oriented perpendicular to the crystal's c-axis rather than parallel to it. If the dome is oriented in between these two directions, an 'off-center' star will be visible, offset away from the high point of the dome.
The Black Star of Queensland, the largest gem-quality star sapphire in the world, weighs 733 carats. The Star of India (weighing 563.4 carats) is thought to be the second-largest star sapphire (the largest blue), and is currently on display at the American Museum of Natural History in New York City. The 182-carat Star of Bombay, located in the National Museum of Natural History, in Washington, D.C., is another example of a large blue star sapphire. The value of a star sapphire depends not only on the weight of the stone, but also the body color, visibility, and intensity of the asterism.