Septarian Nodule

Physical Properties

Hardness: 3.5-4 (Mohs), Color: Brown, grey, yellow (calcite), Luster: Vitreous to dull, Crystal Structure: Trigonal/Orthorhombic, Cleavage: Perfect rhombohedral (calcite phases), Specific Gravity: 2.7-2.9

Formation & Geological History

Formed during the Cretaceous period (approx. 50-70 million years ago) in marine environments. They originated as mud balls that cracked due to dehydration and shrinkage, which were later filled with mineral deposits like calcite and aragonite.

Uses & Applications

Primarily used for decorative purposes, ornamental carvings, lapidary art, jewelry, and as a popular specimen for mineral collectors.

Geological Facts

The name comes from the Latin 'septum' meaning partition, referring to the cracks and separations within the stone. They are also known as 'Dragon Stones' due to their scaly, cracked appearance.

Field Identification & Locations

Identify by looking for distinct 'angular' cracks filled with light-colored minerals inside a darker sedimentary matrix. Often found in Utah, USA, and Madagascar. Collectors look for high contrast between the dark mudstone and bright yellow calcite.

Identified on: 4/21/2026

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