sedimentary

Septarian Nodule (Micro-fragment)

Septarian Nodule / Concretion (CaCO3 + CaMg(CO3)2 + Quartz)

Hardness: 3.5-4.0 (Calcite components) to 7 (Quartz components). Color: Dark brown or black matrix with yellow/gold veins. Luster: Dull matrix with waxy or vitreous veins. Structure: Angular shrinkage cracks filled with secondary minerals.

Hardness: 3
Color: Dark brown or black matrix with yellow/gold veins
Luster: Dull matrix with waxy or vitreous veins

Identified June 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed during the Cretaceous period (approx. 50-70 million years ago) from decomposing organic matter in marine environments. As the clay balls dried and shrank, they cracked, and calcite or aragonite precipitated into the voids.

Uses & applications

Commonly used for lapidary work, decorative paperweights, spiritual/metaphysical collecting, and educational geological specimens.

Geological facts

Septarian comes from the Latin word 'septum' meaning partition, referring to the cracks that divide the concretion. In many specimens, the yellow center is Calcite and the dark exterior is Limestone.

Field identification & locations

Identify by the 'dragon skin' or 'turtle shell' pattern of light-colored veins against a dark mudstone background. Found frequently in Southern Utah and the Gulf of Mexico regions.

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Cone-in-cone structure (Secondary Sedimentary Structure)

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Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Sandstone

Arenite (primarily SiO2)

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