sedimentary
Septarian Nodule
Septarian Concretion (Calcite, Aragonite, and Limestone)
Hardness of 3-4 (due to calcite/aragonite), tan, brown, and grey colors with dark brown or black fractures, dull to vitreous luster, amorphous to microcrystalline structure, specific gravity around 2.6-2.7.
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Physical properties
Hardness of 3-4 (due to calcite/aragonite), tan, brown, and grey colors with dark brown or black fractures, dull to vitreous luster, amorphous to microcrystalline structure, specific gravity around 2.6-2.7.
Formation & geological history
Formed in sedimentary mudstone/concretions around 50 to 100 million years ago (Cretaceous period) when mineral-rich mud balls dried, cracked from shrinking, and were subsequently filled with precipitating minerals like calcite and aragonite.
Uses & applications
Used for ornamental carvings, decorative spheres, polished display specimens, and in lapidary work.
Geological facts
The word septarian comes from the Latin word septem, meaning seven, referring to the cracks that typically divide the patterns into seven points, though the pattern is often more complex.
Field identification & locations
Easily identified by its distinct turtle-shell-like pattern of dark and light intersecting veins. Found worldwide, particularly in Madagascar, Utah, and the UK.
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