GAHNITES (Zinc Spinels)

ZnAl2O4

Spinel is found in a wide range of colours due to the presence of various impurities, and is transparent to almost opaque. Red spinel coloured by chromium and iron is the most popular, although for many years it was thought to be a variety fo ruby. The orange-yellow or range-red variety is called rubicelle (a diminutive of the French word for ruby). Blue spinel (gahnite) is coloured by iron, and less commonly by cobalt.

Spinal occurs in granites and metamorphic rocks, and is often found in association with corundum. Octahedral crystals and waterworn pebbles in a wide range of colours are found in the gem gravels of Burma, Sri :Lanka, and Madagascar. Other localities include Afghanistan, Pakistan, Brazil, Australia, Sweden, Italy, Turkey, the former USSR and the USA.

Synthetic spinel has been manufactured since 1910. It has been used to imitate diamond, or coloured to imitate stones such as aquamarine and zircon. Blue synthetic spinel, coloured by cobalt, has been used to imitate sapphire. The name may derive from the Latin word "spina", meaning little thorn, referring to the sharp points on some crystals.

Hardness: 8

Other characteristics of the Spinel group here