Spinels are composed of magnesium aluminium oxide. Most Spinel is formed due to intense heat from volcanic activity or hydrothermal underwater streams. Origin of name: from Latin spinella meaning little thorn, after crystal shape. Spinels next to ruby and the rare red diamond, is the most expensive of all red gems. With a hardness of 8 and no cleavage planes, natural spinel is a tough and durable gemstone suitable for any kind of jewellery. Unfortunately most Spinel that is sold commercially is synthetic. Sri Lanka, Brazil, Thailand, and United States are most notable sources of natural spinel.
Colour: cobalt blue, red to blue to mauve. Dark green, brown, blackgreen, pink, deep pink with an orange tinge.