Geode

A hollow, rounded rock whose cavity is lined with crystals such as quartz, amethyst or calcite.

Geode specimen — Photo: James St. John, CC BY 2.0, via Wikimedia Commons

How to identify geode

Round, lumpy, cauliflower-like outside.
Feels light for its size (it's hollow).
Crystals or agate bands inside when broken.

Often confused with

Thunderegg
Thundereggs are solid with a star-shaped agate core.
Compare side by side
Concretion
Concretions are solid throughout.
Compare side by side

Where it's found

Keokuk, Iowa
Rio Grande do Sul, Brazil
Artigas, Uruguay
Chihuahua, Mexico

Uses

Display pieces and decor.

Rock tumbling

Not suitable for tumbling.

Did you know?

The geode is Iowa's official state rock.

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