sedimentary

Septarian Nodule (Dragon Stone)

Septarian Concretion (CaCO3 + CaMg(CO3)2 + SiO2)

Hardness: 3.5-4 (Mohs); Color: Brown (siderite/mudstone), yellow (calcite), white (aragonite/quartz); Luster: Waxy to vitreous; Crystal Structure: Trigonal/Orthorhombic mix; Cleavage: Perfect in calcite sections.

Hardness: 3
Luster: Waxy to vitreous

Identified March 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed during the Cretaceous period (50-70 million years ago). They began as sedimentary clay balls that cracked due to dehydration and shrinkage, followed by the infiltration of mineral-rich water that precipitated calcite and aragonite into the cracks.

Uses & applications

Primarily used for decorative purposes, ornamental carvings, high-end interior design slabs, jewelry (cabochons), and as textbook-quality geological specimens for collectors.

Geological facts

Also known as 'Dragon Stone' because the cracked patterns resemble dragon skin. The name 'Septarian' comes from the Latin word 'septum', meaning partition, referring to the cracks and separations within the stone.

Field identification & locations

Identify in the field by looking for rounded, heavy grey mudstone nodules with visible angular protruding patterns. Commonly found in Madagascar, Utah (USA), and parts of the UK. Collectors look for high contrast between the yellow centers and dark outer rinds.

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