Sapphire is the gemstone variety of corundum, an aluminum oxide. The hardness of sapphire is 9, making it one of the hardest gemstones. Sapphire has a vitreous luster and is usually thought of as blue in color, but can be any color except red. It may have "tubelike inclusions" that create the "star" or " catseye" effect which is very desirable as a star sapphire gem.(Chesterman 396). The deep blue sapphire is the color most associated with this gem as the birthstone for September. Major producers and/or cutters of sapphires are Thailand, Sri Lanka, and Burma (Chesterman 397). In the United States sapphires can be found in Montana.
If you want to know more about Sapphire as a birthstone or gemstone check out some of these sites.