The spinels are any of a class of minerals of general formulation A2+B23+O42- which crystallise in the cubic (isometric) crystal system, with the oxide anions arranged in a cubic close-packed lattice and the cations A and B occupying some or all of the octahedral and tetrahedral sites in the lattice. A and B can be divalent, trivalent, or quadrivalent cations, including magnesium, zinc, iron, manganese, aluminium, chromium, titanium, and silicon. Although the anion is normally oxide, structures are also known for the rest of the chalcogenides.
Physical Properties :
Its hardness is 8, its specific gravity is 3.4-4.1 and it is transparent to opaque with a vitreous to dull lustre. It may be colorless, but is usually various shades of red, green, blue, yellow, brown or black. Some spinels are among the most famous gemstones: Among them is the Black Prince's Ruby and the 'Timur ruby' in the British Crown Jewels, and the 'cote de Bretagne' formerly from the French Crown jewels. The Samarian Spinel is the largest known spinel in the world, weighing 500 carats (100 g). The transparent red spinels were called spinel-rubies or balas-rubies. In the past, before the arrival of modern science, spinels and rubies were equally known as rubies. After the 18th century the word ruby was only used for the red gem variety of the mineral corundum and the word spinel became used.The ancient name for Badakhshan, a region in central Asia resided in the upper valley of the Kokcha River, one of the principal tributaries of the Oxus River. The Badakshan province was for centuries the main source for red and pink spinels.
Natural Occurrence :
Sri Lanka, Thailand, Burma and Afghanistan.
Available Colors :
Red, pink, violet, blue, green, aqua, orange, yellow, brown, and black. Rarely white or colorless.