What is Spinel?
Spinel is a cubic magnesium aluminium oxide and a respected gemstone, famous for vivid red and blue colours as well as sharp octahedral crystals.
Mineralogy and crystal structure
Reference formula: MgAl2O4. Spinel has a cubic structure and is distinct from ruby even when its red colour is similar. Colour, fluorescence, inclusions and natural or laboratory origin are important in the gem trade. Spinel is classified with oxides and has a cubic crystal system. Typical hardness is 7.5–8 on the Mohs scale and specific gravity is approximately 3.5–4.1.
Colour, lustre and habit
Typical colours include red, pink, blue, violet, black, orange. The usual octahedral, granular, massive habit and vitreous lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Spinel forms in or is associated with marbles, metamorphic rocks, mafic rocks and alluvial gem deposits. Important documented localities include Myanmar, Sri Lanka, Tanzania, Vietnam, Tajikistan, Madagascar and Afghanistan.
The once-misidentified royal gem
Spinel has moved from being mistaken for ruby to being valued in its own right. Strong red, cobalt-blue and vivid pink stones combine daily-wear durability with growing collector demand.
Collecting and care
Clean with warm soapy water and protect faceted stones from hard impact. Ask for an independent report when colour and origin make the piece valuable.
