Septarian Nodule (Yellow Calcite in Limestone)

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.

Identified on: 5/11/2026

Mode: Standard