sedimentary
Septarian Nodule
Septarian Nodule (Mixture of Calcite, Aragonite, and Limestone/Clay)
Hardness: 3.5-4 (Mohs scale); Color: Yellow (calcite), Brown (aragonite), Gray (limestone); Luster: Greasy to vitreous when polished; Crystal structure: Trigonal/Orthorhombic; Specific gravity: 2.6-2.8
- Hardness
- 3
- Color
- Yellow (calcite), Brown (aragonite), Gray (limestone)
- Luster
- Greasy to vitreous when polished
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Physical properties
Hardness: 3.5-4 (Mohs scale); Color: Yellow (calcite), Brown (aragonite), Gray (limestone); Luster: Greasy to vitreous when polished; Crystal structure: Trigonal/Orthorhombic; Specific gravity: 2.6-2.8
Formation & geological history
Formed as concretions in seafloors during the Cretaceous period (approx. 50-70 million years ago). Dehydration and cracking of clay nodules were later filled with minerals like calcite and aragonite.
Uses & applications
Primarily used as decorative display pieces, spheres, bookends, and in jewelry (cabochons). Highly valued by mineral collectors for its unique 'turtle back' pattern.
Geological facts
The name 'Septarian' comes from the Latin word 'septum', meaning partition, referring to the cracks and separations within the stone. They are also colloquially known as 'Dragon Stones'.
Field identification & locations
Identified by distinct angular partitions or cracks filled with yellow/brown minerals within a gray host rock. Common in Utah (USA) and Madagascar. Collectors look for high contrast and intact crystal centers.
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