Chemical composition -- Magnesium aluminate.
Color -- Red, blue, green, purple, orange, gray, brown, near colorless.
Optics -- R.I. 1.72. Isometric.
Durability -- Hardness 7.5-8.
Crystal structure -- Isometric (cubic).
Specific Gravity -- 3.58-3.63.
Sources -- Burma, Thailand, Cambodia, Afghanistan, Sri Lanka (Ceylon), Russia, U.S., etc.
Spinel has often been confused with rubyand sapphire, but it provides many fine gems in its own right. Some famous large "rubies," such as the Black Prince's Ruby and the Timur Ruby in the British Crown Jewels are actually spinels. Fine large stones are rare and expensive, but smaller stones are quite abundant. Unfortunately, spinel's reputation has suffered due to the widespread use of inexpensive synthetic spinel, and many people do not realize that natural spinel is a very desirable gemstone in its own right.