Star corundum can only be found in small percentages of corundum on the market. As faceted corundum typically sells for more per carat than star corundum fashioned as a cabochon, only those of exceptional body color and outstanding asterism are left untreated and sold as stars.
My favourite stones are those with asterisms like this black star sapphire with a 12 point asterism. The star radiates when in direct sunlight or under a single light source. Stones are cut into cabochon shapes to best display the star. Ancient Greeks highly valued stones with stars, regarding them as powerful love charms. http://www.fashionaccessoryshop.com/colored-precious-stones-emeralds-sapphires-rub.html
De Long Star Ruby (Rubí Estrella). Almacenado en el Museum of Natrual History de Nueva York. 100.32 kilates, de Burma. Fue robado del museo en 1964 y rucuperado después de pagar un rescate de 25,000USD. Fue encontrado en una cabina telefónica.
Star corundum is a type of corundum that exhibits a star-like phenomenon known as asterism, caused by reflections from tiny, needle-like inclusions that are oriented in several specific directions. The finest star corundum is semi-transparent, of distinct star which is centered on the top of the stone and visible from a reasonable distance under luminescent light. Asterism mostly appears in white, it is rare and valuable if star presents the same color as the body color of the stone.
Star Ruby from Burma. Star rubies and sapphires are not as rare as you may think. Star rubies and star sapphires are gemstones that exhibit a star-like phenomenon known as asterism. Star gems contain intersecting needle-like inclusions (often the mineral rutile, a mineral composed primarily of comprised of titanium dioxide) that cause the appearance of a six-rayed 'star'-shaped pattern when viewed with a single overhead light source. To cause a star, the rutile needles form in parallel…
Purple 12-ray star sapphire, 8.13 ct, 11.78 x 10.50 x 6.28 mm. Unlike this one, such stones often are glass-filled. For a brief report on the phenomenon, see “Twelve-rayed star sapphire of interest” by Garry DuToit, GIA Laboratory, Bangkok. (Photo: Jeff Scovil)
The typical size range for star rubies is 1ct to 10cts, but much larger stones exist. One of the largest fine-quality star rubies on public display is the Smithsonian Institution's 137-ct Rosser Reeves Ruby