Iolite

Gem cordierite, a violet-blue stone that changes color dramatically depending on viewing direction.

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

How to identify iolite

Violet-blue from one side, pale yellow-gray or clear from another.
Hardness 7–7.5.
Light for a blue gem.

Often confused with

Sapphire
Sapphire is much harder and heavier.
Compare side by side
Tanzanite
Tanzanite is softer and heavier.
Compare side by side

Where it's found

India
Sri Lanka
Madagascar
Tanzania

Uses

Gemstones.

Rock tumbling

Great for tumbling.

Did you know?

Turning a crystal of iolite can make it go from deep blue to nearly colorless — a striking pleochroism.

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