sedimentary
Septarian Nodule Segment (Commonly known as Dragon Stone or Lightning Stone)
Septarian Nodule (CaCO3 / Hydrated Calcium Carbonate)
Hardness: 3.5-4 (Mohs); Color: Creamy tan to beige with brown calcite/aragonite veining; Luster: Waxy to dull; Crystal structure: Trigonal (as calcite veins/mudstone matrix); Cleavage: Rhombohedral along veins; Specific Gravity: 2.6-2.8
- Hardness
- 3
- Color
- Creamy tan to beige with brown calcite/aragonite veining
- Luster
- Waxy to dull
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Physical properties
Hardness: 3.5-4 (Mohs); Color: Creamy tan to beige with brown calcite/aragonite veining; Luster: Waxy to dull; Crystal structure: Trigonal (as calcite veins/mudstone matrix); Cleavage: Rhombohedral along veins; Specific Gravity: 2.6-2.8
Formation & geological history
Formed during the Cretaceous period (approx. 50-70 million years ago) from mud balls on ancient seafloors. The mud shrank and cracked (septaria), and minerals like calcite and aragonite precipitated into the fissures from groundwater.
Uses & applications
Used primarily for lapidary work (cabochons), interior decoration (polished bookends or spheres), and as metaphysical/collectible specimens.
Geological facts
The name comes from the Latin word 'septum', meaning partition, referring to the cracks that divide the specimen. They are often found containing hollow cavities lined with tiny crystals.
Field identification & locations
Identify in the field by their distinctive 'crackle' or 'brain-like' surface pattern on a rounded nodule. Commonly found in Utah (USA), Madagascar, and the coast of England. For collectors, look for high contrast between the host rock and the crystal veins.
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