sedimentary
Septarian Nodule
Septarian concretion (composition: Calcium carbonate, Aragonite, and Siderite/Baryte)
Hardness: 3.5-4 (Mohs scale); Color: Yellow (calcite), Brown (aragonite), Gray (limestone shell); Luster: Waxy to vitreous; Crystal structure: Trigonal/Orthorhombic; Specific gravity: 2.6-2.9
- Hardness
- 3
- Color
- Yellow (calcite), Brown (aragonite), Gray (limestone shell)
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 3.5-4 (Mohs scale); Color: Yellow (calcite), Brown (aragonite), Gray (limestone shell); Luster: Waxy to vitreous; Crystal structure: Trigonal/Orthorhombic; Specific gravity: 2.6-2.9
Formation & geological history
Formed during the Cretaceous period (50-70 million years ago) through the dehydration of clay-rich mud balls on sea floors. The mud balls dried and cracked, and the cracks were later filled with minerals like calcite and aragonite.
Uses & applications
Commonly used as decorative objects, paperweights, sculptures, and jewelry. Highly valued for display in mineral collections.
Geological facts
The name 'Septarian' comes from the Latin word 'septum', meaning partition, referring to the cracks that divide the concretion. They are also known as 'Dragon Stones' due to their resemblance to dragon skin or scales.
Field identification & locations
Identified by its distinctive 'honeycomb' or cracked pattern of yellow calcite and brown aragonite set in a gray or tan background. Commonly found in Utah, USA and Madagascar. It will react and fizz when exposed to dilute hydrochloric acid.
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