Spinel

Spinel has played an important part in gem history. Prior to the last century, it was impossible to distinguish from ruby and sapphire once it was cut. The “Black Prince’s Ruby” and the “Timur Ruby” in the British crown jewels are actually spinels.

Spinel comes in every color of the rainbow, from strong, deep colors to very light pastels. They are found on every continent, but the primary sources are Sri Lanka, and Burma.

While sometimes very light, natural gems are never truly colorless. Colorless spinels are beautiful and make a nice diamond substitute. However, when you find one, the fact that it is colorless proves it is synthetic.

Spinel is actually a large group of minerals. Gahnite, hercynite, ceylonite, picotite, and galaxite are all part of the spinel group. These are very dark and are rarely used as gems. They are all isometric oxides of magnesium, iron and zinc, with traces of aluminum and other elements.

There is a solid state solution between spinel (MgAl2O4) and gahnite, (ZnAl2O4). The intermediate species is known as gahnospinel and has a formula of (MgZn)Al2O4. Unlike most series, pure spinel is much more common than its blend. Gahnite is not a gem mineral….