sedimentary
Septarian Nodule
Septarian Concretion (CaCO3 with Calcite/Aragonite and Clay/Mudstone)
Hardness: 3 to 4 (calcite veins), ~5-6 (grey matrix). Colors: Grey mudstone, yellow calcite crystals, brown aragonite rims. Luster: Earthy (matrix) to vitreous/resinous (vein minerals). Structure: Microcrystalline matrix with trigonal/orthorhombic mineral vein infillings.
- Hardness
- 3 to 4 (calcite veins), ~5-6 (grey matrix)
- Luster
- Earthy (matrix) to vitreous/resinous (vein minerals)
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Physical properties
Hardness: 3 to 4 (calcite veins), ~5-6 (grey matrix). Colors: Grey mudstone, yellow calcite crystals, brown aragonite rims. Luster: Earthy (matrix) to vitreous/resinous (vein minerals). Structure: Microcrystalline matrix with trigonal/orthorhombic mineral vein infillings.
Formation & geological history
Formed during the Cretaceous period (50 to 70 million years ago) in marine environments. Dehydrating and shrinking mud nodules formed internal contraction cracks, which were later filled with calcite, aragonite, and barite precipitated from mineral-rich fluids.
Uses & applications
Highly popular among mineral collectors, used for lapidary carving, polished display slabs, decorative bookends, and holistic/metaphysical uses.
Geological facts
The word septarian is derived from the Latin word 'septum', meaning partition or wall, referring to the cracks that divide the inner sections of the stone. They are often called 'Dragon Stones' due to their reptilian pattern.
Field identification & locations
Identified by the distinct geometric pattern of grey angular mudstone blocks surrounded by brown aragonite borders and filled with yellow calcite. Commonly found in Utah (USA), Madagascar, England, and Morocco.
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