Opal

Hydrated silica with no crystal structure. In precious opal, stacked microscopic spheres split light into flashing rainbow patches.

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

How to identify opal

Flashes of spectral color that shift as you turn it.
Waxy to glassy luster.
Light in weight for a gemstone.
Common opal lacks color play and looks milky.

Often confused with

Labradorite
Labradorite flashes as one sheet of color from one angle.
Compare side by side

Where it's found

Coober Pedy, Australia
Lightning Ridge, Australia
Wollo, Ethiopia
Querétaro, Mexico

Uses

Gemstones.

Rock tumbling

Not suitable for tumbling. Contains water and can crack from heat or drying.

Did you know?

Many residents of Coober Pedy, the opal capital, live in underground homes to escape the heat.

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