Septarian Nodule

A clay-rich concretion whose shrinkage cracks filled with yellow calcite.

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

How to identify septarian nodule

Gray body crossed by yellow-brown calcite veins.
Veins wider in the center, thinning outward.
Fizzes in acid.

Often confused with

Concretion
Plain concretions lack the crystal-filled cracks.
Compare side by side
Geode
Geodes are hollow and crystal-lined.
Compare side by side

Where it's found

Kanab, Utah
Mahajanga, Madagascar
Dorset, England

Uses

Polished halves and spheres.

Rock tumbling

Can be tumbled with care.

Did you know?

The name comes from Latin septum, 'partition', for the cracks dividing the inside.

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