Gemstone Series: Spinel

Spinel is a beautiful, and in my opinion, greatly underappreciated gemstone. It forms in a large variety of colors (red, pink, blue, violet, yellow, orange, green, black, brown), and it is a very durable stone. It has a hardness of 8 on Moh’s hardness scale, and it does not fracture easily. Spinel is a magnesium aluminum oxide (MgAl2O4).

Spinel is actually a family of related minerals. Types of gem-quality spinel include flame spinel, balas spinel, pleonaste, hercynite, gahnite, gahnospinel, and picolite (chrome spinel).

Historically, spinel was not known as a separate mineral. It was usually called ruby, and many famous rubies were later found to actually be spinel. The Black Prince’s Ruby in the English Crown and the Timur Ruby in the English Crown Jewels are two such examples.

Spinel is found in placer deposits, along with ruby, in many locations around the world. Important sources include Burma, Cambodia, and Sri Lanka. Like ruby, spinel is a metamorphic mineral found in limestones, dolostones, and low-silica alkali igneous rocks.

Synthetic spinel was first created in 1919. Synthetic spinel has been used as a imitation for many gemstones including diamond, ruby, and sapphire.

Google image results for spinel.
Spinel entries on webmineral and mineral gallery.