sedimentary
Septarian Nodule
Septarian Concretion (Calcite, Aragonite, and Limestone)
AI-generated identification · may be incorrectHardness 3-4 on Mohs scale; multicolored brown, yellow, and grey with contrasting white or yellow calcite veins; dull to vitreous luster; massive crystal structure.
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Physical properties
Hardness 3-4 on Mohs scale; multicolored brown, yellow, and grey with contrasting white or yellow calcite veins; dull to vitreous luster; massive crystal structure.
Formation & geological history
Formed in sedimentary mudstone layers during the Cretaceous period roughly 50 to 100 million years ago through the desiccation and cracking of concretion nodules, later filled with mineral-rich water.
Uses & applications
Popular among lapidaries and collectors for making decorative spheres, cabochons, carved display pieces, and bookends.
Geological facts
The name originates from the Latin word septum, meaning partition, referring to the characteristic crack patterns inside that resemble turtle shells.
Field identification & locations
Easily identified by distinctive spiderweb-like calcite fracture networks visible upon cutting or weathering; found globally in marine sedimentary deposits.
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