sedimentary

Septarian Nodule (Dragon Stone)

Septarian concretion (composition: CaCO3 - Calcite, Aragonite, and Siderite/Limestone)

Hardness: 3.5-4.0 (Mohs scale); Color: Black/brown (siderite or limestone), Yellow (calcite), Brown (aragonite); Luster: Vitreous to dull; Structure: Microcrystalline with radial shrinkage cracks filled with crystals.

Hardness: 3
Luster: Vitreous to dull

Identified March 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed during the Cretaceous period (50-70 million years ago) in marine environments. Mud balls formed by chemical attraction around organic matter, dried, cracked, and then mineral-rich waters filled the cracks with calcite and aragonite.

Uses & applications

Primarily used for ornamental purposes, lapidary carvings, jewelry (cabochons), and as a popular display specimen for mineral collectors.

Geological facts

They are often nicknamed 'Dragon Stones' because their cracked, geometric patterns resemble dragon scales. They are unique because they are a combination of different minerals forming a single rock unit through a shrinking process.

Field identification & locations

Identify by the distinct 'lightning bolt' or 'turtle shell' patterns of yellow/white veins against a dark background. Commonly found in Utah (USA) and Madagascar. In the field, look for round, gray mudstone nodules that often have a distinct cracked core.

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