sedimentary
Septarian Nodule
Septarian Concretion (CaCO3 + Hydrated SiO2)
Hardness: 3.5-4; Color: Gray, tan, brown, yellow; Luster: Waxy to earthy; Structure: Microcrystalline with distinct shrinkage cracks filled with calcite or aragonite.
- Hardness
- 3
- Color
- Gray, tan, brown, yellow
- Luster
- Waxy to earthy
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Physical properties
Hardness: 3.5-4; Color: Gray, tan, brown, yellow; Luster: Waxy to earthy; Structure: Microcrystalline with distinct shrinkage cracks filled with calcite or aragonite.
Formation & geological history
Formed during the Cretaceous period (50-70 million years ago) in marine environments. Decomposing organic matter caused sediment to clump, and as it dried, it cracked. Minerals later seeped into the cracks.
Uses & applications
Primarily used for ornamental purposes, lapidary arts, jewelry, and as a popular display specimen for collectors.
Geological facts
Also known as 'Dragon Stones' due to the patterns resembling dragon skin. The name comes from the Latin word 'septum', meaning partition, referring to the cracks that divide the concretion.
Field identification & locations
Identify by the distinct 'turtle shell' or partitioned pattern on the surface or inside. Commonly found in Utah (USA), Madagascar, and Morocco. Look for rounded nodules in shale beds.
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