sedimentary
Septarian Nodule (Dragon Stone)
Septarian concretion (Complex of Calcite, Aragonite, and Limestone)
Hardness: 3.5-4 (Mohs); Color: Grey/Brown (limestone), Yellow (calcite), Brown (aragonite); Luster: Vitreous to dull; Crystal structure: Trigonal/Orthorhombic; Specific gravity: 2.7.
- Hardness
- 3
- Color
- Grey/Brown (limestone), Yellow (calcite), Brown (aragonite)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 3.5-4 (Mohs); Color: Grey/Brown (limestone), Yellow (calcite), Brown (aragonite); Luster: Vitreous to dull; Crystal structure: Trigonal/Orthorhombic; Specific gravity: 2.7.
Formation & geological history
Formed during the Cretaceous period (50-70 million years ago) from volcanic eruptions that trapped sea life in mud balls, which then contracted and cracked, allowing mineral-rich fluids to fill the cavities.
Uses & applications
Used primarily in lapidary work for ornamental carvings, spheres, bookends, and high-end jewelry; also highly valued as display specimens for collectors.
Geological facts
Also known as 'Dragon Stones' due to their scaly appearance. They are often found with hollow centers containing druzy crystals, making them technically a type of geode/concretion hybrid.
Field identification & locations
Identify by the distinctive 'patterned' segments of yellow calcite against grey matrix. Commonly found in Utah (USA) and Madagascar. To identify in the field, look for round mud-balls that sound hollow when struck.
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