sedimentary
Septarian Nodule (Septarian Dragon Stone)
Septarian concretion (composition: Calcite CaCO3, Aragonite CaCO3, and Limestone/Clay)
Hardness: 3.5-4 (Mohs); Color: Yellow (calcite), Brown (aragonite), Grey (limestone); Luster: Vitreous to dull; Crystal structure: Trigonal/Orthorhombic; Specific Gravity: 2.6-2.8. Features distinctive cracked 'mud' patterns filled with minerals.
- Hardness
- 3
- Color
- Yellow (calcite), Brown (aragonite), Grey (limestone)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 3.5-4 (Mohs); Color: Yellow (calcite), Brown (aragonite), Grey (limestone); Luster: Vitreous to dull; Crystal structure: Trigonal/Orthorhombic; Specific Gravity: 2.6-2.8. Features distinctive cracked 'mud' patterns filled with minerals.
Formation & geological history
Formed during the Cretaceous period (approx. 50-70 million years ago) when volcanic eruptions killed marine life that sank to sea floors, creating mud balls. As the oceans receded and the mud dried, they cracked; minerals like calcite then leached into the cavities.
Uses & applications
Primarily used for lapidary work, decorative home decor, spheres, carvings, and as popular specimens for mineral collectors due to their unique aesthetic patterns.
Geological facts
Also known as 'Dragon Stones' because the geometric patterns resemble dragon skin. Madagascar and Utah (USA) are the most famous sources for high-quality, colorful specimens with thick calcite veins.
Field identification & locations
Identify in the field by looking for rounded, heavy concretions with a cracked, 'turtle-back' exterior. They are often found in areas with exposed shale or clay beds. Collectors should look for intact nodules that can be cut to reveal internal cavities.
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