sedimentary

Septarian Nodule (Dragon Stone)

Septarian concretion (CaCO3 with Aragonite and Calcite)

Hardness: 3.5-4 (Mohs scale); Color: Yellow (calcite), Brown (aragonite shell), Grey (limestone exterior); Luster: Vitreous to dull; Crystal structure: Trigonal/Orthorhombic; Cleavage: Perfect rhombohedral in calcite areas.

Hardness: 3
Luster: Vitreous to dull

Identified March 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed roughly 50 to 70 million years ago during the Cretaceous period. These nodules started as mud balls on ancient seafloors which cracked as they dried and shrunk, with minerals like calcite later precipitating into the cracks.

Uses & applications

Primarily used for ornamental purposes, lapidary arts (cabochons, spheres), home decor, and as a popular metaphysical or fossil-enthusiast collector's item.

Geological facts

Also known as 'Dragon Stones' due to the scaled appearance of the cracked patterns. The name 'Septarian' comes from the Latin 'septum' meaning partition, referring to the cracks that divide the concretion.

Field identification & locations

Identify in the field by looking for rounded, heavy grey nodules that reveal a 'star' or 'honeycomb' internal pattern when cracked open. Common locations include Utah (USA), Madagascar, and the United Kingdom.

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