Septarian Nodule (Dragon Stone)

Physical Properties

Hardness: 3.5-4 (on Mohs scale); Color: Black or brown (siderite/clay), yellow (calcite), white (aragonite); Luster: Vitreous to dull; Crystal structure: Trigonal (calcite); Cleavage: Perfect rhombohedral in calcite portions.

Formation & Geological History

Formed roughly 50 to 70 million years ago during the Cretaceous period. They began as mud balls on ancient seafloors. Volcanic activity caused the mud to crack and shrink, which was later filled by mineral-rich waters that deposited calcite and aragonite.

Uses & Applications

Primarily used as ornamental stones for display, decorative carvings, lapidary cabochons, and metaphysical collecting.

Geological Facts

Also known as 'Dragon Stones' due to their cracked skins and inner crystalline cores. The name comes from 'septum' (meaning partition) in Latin, referring to the cracks that divide the stone's sections.

Field Identification & Locations

Field identification involves looking for rounded, greyish limestone concretions that, when broken or polished, reveal yellow/brown crystalline patterns inside. Commonly found in Utah (USA) and Madagascar.

Identified on: 4/29/2026

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