Agate

Banded chalcedony — quartz made of microscopic crystals — that fills cavities in volcanic rock layer by layer. Light passes through the bands when held up to the sun.

How to identify agate

Concentric or parallel bands, often in red, orange and white.
Translucent at the edges when backlit.
Waxy surface on rough, weathered pieces ('pitted' rind).
Hard enough to scratch glass.

Often confused with

Jasper
Jasper is fully opaque; agate glows when you shine a flashlight through it.
Compare side by side
Chert
Chert is opaque and lacks agate's neat concentric banding.
Compare side by side

Where it's found

Lake Superior shores
Rio Grande do Sul, Brazil
Botswana
Chihuahua, Mexico

Uses

Tumbled stones, cameos, mortars and pestles for labs.

Rock tumbling

Great for tumbling.

Did you know?

The Lake Superior agate is Minnesota's state gemstone.

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