Spinel

A hard magnesium aluminum oxide that forms sharp octahedral crystals — long confused with ruby.

Spinel specimen — Photo: Robert M. Lavinsky, CC BY-SA 3.0, via Wikimedia Commons

How to identify spinel

Sharp eight-sided octahedrons, often in marble.
Hardness about 8.
Red, pink, blue or purple with a bright glassy luster.

Often confused with

Ruby
Ruby is harder, forms hexagonal crystals and is doubly refractive.
Compare side by side
Garnet
Garnet forms rounded dodecahedra.
Compare side by side

Where it's found

Mogok, Myanmar
Badakhshan, Tajikistan
Sri Lanka
Vietnam

Uses

Gemstones.

Rock tumbling

Great for tumbling.

Did you know?

The 'Black Prince's Ruby' in Britain's Imperial State Crown is actually a spinel.

Think you could spot it from a blurry close-up?

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