sedimentary

Septarian Nodule

Septarian Nodule (Calcite, Aragonite, and Limestone/Claystone)

Hardness: 3.5 to 4; Color: Yellow/brown centers with dark brown lines and tan matrix; Luster: Waxy to sub-vitreous; Structure: Microcrystalline with distinct shrinkage cracks (septaria); Cleavage: Perfect rhombohedral in calcite portions.

Hardness: 3
Color: Yellow/brown centers with dark brown lines and tan matrix
Luster: Waxy to sub-vitreous

Identified July 15, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed during the Cretaceous period approximately 50 to 70 million years ago. These started as muddy concretions around organic matter that dried out and cracked, with the cracks later filling with minerals like calcite and aragonite.

Uses & applications

Primarily used as a decorative stone, in jewelry (cabochons), as metaphysical palm stones, and for scientific/collector displays.

Geological facts

Also known as Dragon Stones due to their scaly appearance, they are unique because they were formed through a combination of chemical precipitations and mechanical shrinking processes.

Field identification & locations

Identify by looking for the distinct 'lightning bolt' or spiderweb patterns of dark mineral veins against a lighter host rock. Major deposits are found in Utah, USA and Madagascar.

Other sedimentary specimens

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Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Fossiliferous Concretion

Septarian Concretion containing Brachiopods/Crinoids

fossil

Shale

Shale (clastic sedimentary rock)

sedimentary

Brown Sandstone (River Rock)

Arenite

sedimentary

Mudstone

Argillite / Siliciclastic sedimentary rock

sedimentary

Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

sedimentary