sedimentary

Septarian Nodule with Calcite

Septarian Concretion (CaCO3 with internal calcite crystals)

Hardness: 3-4 on Mohs scale (for calcite); Color: Brown, yellow, grey with yellow/amber crystal centers; Luster: Vitreous to dull; Crystal structure: Trigonal (calcite); Cleavage: Perfect rhombohedral cleavage on calcite; Specific gravity: 2.6-2.7

Hardness: 3-4 on Mohs scale (for calcite)
Color: Brown, yellow, grey with yellow/amber crystal centers
Luster: Vitreous to dull

Identified August 4, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in sedimentary muds and shales approximately 50 to 150 million years ago during the Cretaceous period, where shrinking mud caused radial cracks that later filled with mineral-rich water precipitating calcite.

Uses & applications

Used for ornamental carvings, spheres, lapidary art, display specimens, and in metaphysical practices.

Geological facts

The word 'septarian' comes from the Latin word 'septem,' meaning seven, referring to the pattern of cracks that typically divide the nodules into seven or more pointed segments.

Field identification & locations

Easily identified by its distinctive turtle-shell-like exterior patterns and inner cavities lined with yellow or brown calcite crystals. Found prominently in regions like Madagascar and Utah, USA.

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