Spinel is the magnesium aluminium member of the large spinel group of minerals. It has an imperfect octahedral cleavage and a conchoidal fracture. Its hardness is 8 on Moh’s scale of mineral hardness.

It varies from transparent to opaque and from vitreous to dull luster. It may be colorless or exist in various shades of red, blue, green, yellow, brown and black. A unique natural white spinel was found in Sri Lanka.

Spinels rank among the most famous gemstones. The Black Prince’s Ruby and the Timur Ruby are in the British Crown jewels. The ‘cote de Bretagne’ belonged to the former French Crown jewels. The largest known spinel in the world is Samarian Spinel weighing 500 carats or a massive 100 grams.

The transparent red spinels were called spinel-rubies or balas rubies. In the past both spinels and rubies were called as rubies. After the 18th century the word ruby denotes the red gem variety of the mineral corundum and the word spinel denotes the others.

Balas ruby is an old name for a rose-tinted variety. “Balas” is derived from Balascia, the ancient name forBadakhshan province – the main source for red and pink spinels for centuries.

True spinel exist in the gemstone bearing gravel of Sri Lanka and in the lime stones of the Badakshan Province (in modern day Afghanistan) and in Burma.

Recently gem quality spinels were found in Vietnam, Tanzania, Kenya and Madagascar. Spinel is found as a metamorphic mineral. It is also a primary mineral in rare mafic igneous rocks. Combination with aluminium oxide forms corundum while combination with magnesia forms spinel. This explains why ruby and spinel are often found together.