sedimentary
Septarian Nodule
Septarian Concretion (CaCO3 with Siderite/Calcite)
Hardness: 3.5-4 (Mohs); Color: Brown, tan, and gray with yellow/white veins; Luster: Dull to earthy (matrix), Vitreous (veins); Structure: Concretions with dehydration cracks.
- Hardness
- 3
- Color
- Brown, tan, and gray with yellow/white veins
- Luster
- Dull to earthy (matrix), Vitreous (veins)
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Physical properties
Hardness: 3.5-4 (Mohs); Color: Brown, tan, and gray with yellow/white veins; Luster: Dull to earthy (matrix), Vitreous (veins); Structure: Concretions with dehydration cracks.
Formation & geological history
Formed during the Cretaceous period (approx. 50-70 million years ago) in marine environments. Clay balls shrank and cracked through dehydration, and minerals like calcite precipitated into the cracks.
Uses & applications
Used primarily for ornamental items, interior design, jewelry (cabochons), and as museum-quality display specimens for collectors.
Geological facts
The name 'Septarian' comes from the Latin word 'septum', meaning partition, referring to the cracks that divide the concretion into distinct sections. They are often called 'Dragon Stones'.
Field identification & locations
Identified by distinct 'turtle-back' patterns of cracks on the surface or internal chambers filled with crystals. Commonly found in Utah, USA, and Madagascar.
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