Spinel is a magnesium aluminum oxide mineral (MgAl2O4) known for its striking colors, high clarity, and durability. It’s part of the cubic crystal system, meaning it often forms in well-shaped octahedral crystals.

Here’s a detailed description:

Appearance & Color

• Can be red, pink, orange, violet, blue, purple, or even colorless.

• The most prized are vivid reds (often mistaken for ruby in history) and intense cobalt blues.

• Transparent to translucent, with a glassy (vitreous) luster.

Physical Properties

• Hardness: 8 on the Mohs scale — very durable.

• Cleavage: None (breaks with a conchoidal fracture, like glass).

• Refractive Index: ~1.718, giving it notable brilliance.

• Specific Gravity: ~3.58–4.06.

Geological Occurrence

• Forms in metamorphic rocks like marble and in alluvial deposits where it’s found as water-worn crystals.

• Major sources: Myanmar (Burma), Sri Lanka, Vietnam, Tanzania, Afghanistan.

Special Notes

• Historically, famous “rubies” such as the Black Prince’s Ruby in the British Crown Jewels are actually red spinel.

• Synthetic spinel has been used in jewelry and even as a durable watch glass.