sedimentary
Septarian Nodule (Yellow Calcite in Limestone)
Septarian Concretion (CaCO3 with Aragonite and Calcite)
Hardness: 3.5-4.0; Color: yellow, brown, gray, black; Luster: vitreous to resinous; Crystal structure: Trigonal (calcite); Fracture: Conchoidal to uneven; Specific Gravity: 2.7
- Hardness
- 3
- Color
- yellow, brown, gray, black
- Luster
- vitreous to resinous
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Physical properties
Hardness: 3.5-4.0; Color: yellow, brown, gray, black; Luster: vitreous to resinous; Crystal structure: Trigonal (calcite); Fracture: Conchoidal to uneven; Specific Gravity: 2.7
Formation & geological history
Formed during the Cretaceous period (50-70 million years ago) through the dehydration and cracking of clay nodules, which were then filled by pulsating mineral-rich fluids (calcite and aragonite).
Uses & applications
Primarily used as decorative display pieces, for crystal healing, or secondary use in meditation and lapidary arts like spheres and eggs.
Geological facts
Also known as 'Dragon Stones' due to their cracked, egg-like appearance. They are complex concretions that can contain calcite, aragonite, limestone, and occasionally pyrite.
Field identification & locations
Identify by the distinctive 'cracked' pattern (septaria) where yellow calcite fills dark brown limestone. Common in Utah (USA) and Madagascar. Look for the contrast between the yellow core and darker outer rind.
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