Onyx

Chalcedony with straight, parallel bands, classically black and white. Most solid black onyx is dyed.

Onyx specimen — Photo: W.carter, CC BY 4.0, via Wikimedia Commons

How to identify onyx

Straight, parallel bands — not curved like most agate.
Hard (scratches glass), waxy polish.
Uniform jet-black stones are usually dyed chalcedony.

Often confused with

Obsidian
Obsidian is softer glass and lacks banding.
Compare side by side
Agate
Agate bands are usually curved and concentric.
Compare side by side

Where it's found

Brazil
India
Uruguay

Uses

Cameos, beads and inlay.

Rock tumbling

Great for tumbling.

Did you know?

'Onyx marble' sold for decor is actually banded calcite — much softer and it fizzes in acid.

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