Fascinating gemstone which has been mistakenly identified and used as a substitute for all kinds of other gems because of its wide variety of colors. The "Black Prince's Ruby" in the British crown jewels is actually a spinel.

Completely pure spinel is colorless and has been used to as a diamond substitute in jewelry. Colored spinels get their color from impurities; the most valuable red and blue ones are hard to tell from ruby and sapphire. The natural stone also comes in green, violet, black, and orange. Occasional spinels with asterisms have been found.

Synthetic spinel has been manufactured since 1915 and is commonly used in cheap jewelry (Joel Arem's Gems specifically mentions 'class rings and inexpensive birthstone jewelry, usually (erroneously) labeled in quotes, such as "tourmaline" or "topaz."' With a rating on the Mohs hardness scale of 8, spinel works well in jewelry.