sedimentary

Septarian Nodule (Dragon Stone)

Septarian Concretion (CaCO3 with Siderite and Calcite)

Hardness: 3.5-4 (Mohs scale); Color: Yellow (calcite), Brown (aragonite), Gray (limestone); Luster: Greasy to vitreous; Crystal Structure: Hexagonal/Rhombohedral; Cleavage: Perfect rhombohedral in calcite portions.

Hardness: 3
Color: Yellow (calcite), Brown (aragonite), Gray (limestone)
Luster: Greasy to vitreous

Identified March 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed during the Cretaceous period (50-70 million years ago). They originated as mud balls that cracked due to dehydration and shrinkage, which then filled with minerals like calcite and aragonite while submerged on the ocean floor.

Uses & applications

Primarily used for ornamental purposes, lapidary art, jewelry (cabochons), and as display specimens for collectors due to their unique 'dragon skin' patterns.

Geological facts

The name comes from the Latin 'septum' (partition) or 'saeptum' (enclosure), referring to the cracks that divide the specimen. They are often called 'Dragon Stones' because the patterns resemble dragon scales.

Field identification & locations

Identify in the field by looking for rounded, gray limestone nodules that exhibit a 'turtle shell' pattern of cracks when broken open. Most commonly found in Utah, USA, and Madagascar.

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