sedimentary

Septarian Nodule Geode

Septarian Nodule (Mixture of Calcite, Aragonite, and Limestone/Clay)

Hardness: 3-4 (Calcite portion). Colors: Yellow (Calcite), Brown (Aragonite), Grey (Limestone). Luster: Vitreous to dull. Crystal structure: Trigonal/Hexagonal within voids. Often displays characteristic 'turtle-back' cracking patterns.

Hardness: 3-4 (Calcite portion)
Luster: Vitreous to dull

Identified July 20, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed during the Cretaceous period (50-70 million years ago). They originated as clay balls on ancient seafloors. As they dried, they shrunk and cracked; minerals (Calcite and Aragonite) then precipitated from groundwater into these cracks, filling the voids.

Uses & applications

Primarily used for lapidary work, home decor, large display spheres, and geological collecting. Polished faces highlight the unique internal geometry.

Geological facts

The name 'Septarian' comes from the Latin word 'septum', meaning partition, referring to the cracks that divide the nodule. They are also known as Dragon Stones due to their reptilian appearance.

Field identification & locations

Identify in the field by their rounded, potato-like exterior and unusually heavy weight for their size. When cracked open, the distinct mustard-yellow and dark brown patterns are unmistakable. Major deposits are found in Utah (USA) and Madagascar.

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