sedimentary

Septarian Nodule

Septarian Concretion (Calcite, Aragonite, and Limestone)

AI-generated identification · may be incorrect

Hardness of 3-4 on the Mohs scale for the internal minerals (calcite/aragonite) and around 3 for the limestone host; colors range from brown, yellow, and grey to white; dull to vitreous luster; amorphous overall nodular shape with crystalline internal cavities; specific gravity of approximately 2.6 to 2.7.

Identified August 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in sedimentary environments during the Cretaceous period (roughly 50 to 100 million years ago). They begin as muddy sediments containing organic matter that forms concretions, which subsequently crack from shrinkage (syneresis or drying) and are later filled with mineral-rich groundwater precipitating calcite and aragonite.

Uses & applications

Popular in lapidary arts, sliced and polished as decorative display specimens, carved into decorative objects, and collected by mineral enthusiasts.

Geological facts

The name septarian comes from the Latin word 'septum', meaning partition, referring to the distinctive network of angular cavities or cracks dividing the rock into compartments.

Field identification & locations

Easily identified by its distinct turtle-shell-like pattern of intersecting mineral veins cutting through a rounded, brownish sedimentary concretion. Commonly found in locations such as Utah and Madagascar.