Sapphire is a variety of the species corundum. It's cousin, if you will, is the ruby. Some say a ruby is a red sapphire. No. A ruby is a gem unto itself. While both are similar in chemical and mineral make-up, the additional chromium or iron in the ruby sets it appart as other than a sapphire. Sapphires come in just about every color but red. White sapphires have been used as a diamond substitute for centuries. Star sapphires are beautiful and can come in as many as 18 legged stars. More often you will see four or six stars. Star sapphires are both natural and man -made. The Lindy star sapphire being the best known of the synthetic varieties. When buying a star sapphire the sales person should let you know if it natural or synthetic. There is also a star sapphire process by which an off green sapphire is coated with iron and titanium and heated. Then the stone is again coated with titanium and again heated. This creates a blue colored stone and the star effect. These stones are a muted gray/blue and the spokes of the star are a bit uneven. The star phenomenon is called asterism. This occurs in several gems when light is reflected from sets of minute, oriented, needle-like inclusions. To achieve this effect the stone must be cut into a high, medium, or hollow cabochon. Chatoyancy is also found in sapphires. This is the reflection of light from minute, parallel, needlelike inclusions and creates the cat’s-eye effect. When selecting a sapphire you want to look for the deep royal blue color or a step or two lighter. This is the more valuable. The darker the sapphire the less desirable. Sapphires are often heat treated to lighten their color. Of course there are people who prefer the darker stones. Some midnight blue sapphires make a lovely setting.Sapphires are a 9 on the Moh’s scale. Depending on the other stones used with them, sapphires can be placed in a sonic cleaner.