sedimentary
Septarian Nodule
Septarian Concretion
AI-generated identification · may be incorrectMohs hardness of 3-4 for calcite veins and 5-7 for surrounding limestone; reddish-brown color with yellow calcite infills; dull to earthy luster; amorphous or microcrystalline structure.
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Physical properties
Mohs hardness of 3-4 for calcite veins and 5-7 for surrounding limestone; reddish-brown color with yellow calcite infills; dull to earthy luster; amorphous or microcrystalline structure.
Formation & geological history
Formed in sedimentary mudstone layers during the Cretaceous period through the drying and cracking of mud concretions, later filled with mineral-rich waters.
Uses & applications
Prized by collectors and lapidaries for decorative spheres, bookends, and polished display pieces.
Geological facts
The distinctive crack patterns form when the center of a mud ball shrinks faster than the outer crust, creating mud-filled shrinkage voids.
Field identification & locations
Easily identified by its turtle-shell-like polygonal surface patterns; commonly found in marine shale formations worldwide, particularly in Utah and Madagascar.
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