sedimentary
Septarian Nodule
Septarian Concretion (Calcite, Aragonite, and Limestone)
Hardness of 3-4 (due to calcite/aragonite) to 4 (limestone matrix) on the Mohs scale; colors include brown, yellow, white, and grey; dull to vitreous luster; massive or crystalline structure; specific gravity around 2.6-2.7.
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Physical properties
Hardness of 3-4 (due to calcite/aragonite) to 4 (limestone matrix) on the Mohs scale; colors include brown, yellow, white, and grey; dull to vitreous luster; massive or crystalline structure; specific gravity around 2.6-2.7.
Formation & geological history
Formed in sedimentary environments during the Cretaceous period (approx. 50-100 million years ago) as volcanic ash, mud, and decaying organic matter formed nodules that later dried, cracked, and filled with mineral-rich waters forming crystalline calcite and aragonite veins.
Uses & applications
Used primarily in lapidary arts, decorative items, bookends, sphere carving, and as a popular specimen for mineral collectors.
Geological facts
The word 'septarian' comes from the Latin word 'septem,' meaning seven, referring to the radiating cracks that typically divide the concretion into seven or more parts.
Field identification & locations
Easily identified by its distinctive pattern of angular cavities and contrasting mineral veins intersecting a brownish mudstone/limestone exterior. Commonly found in locations such as Madagascar, Utah, and England.
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