sedimentary

Septarian Nodule (Dragon Stone)

Septarian Concretion (CaCO3 with Siderite and Calcite)

Hardness: 3.5 to 4 on Mohs scale; Color: Brown (siderite), yellow (calcite), and grey (limestone); Luster: Waxy to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: Perfect rhombohedral in calcite portions.

Hardness: 3
Color: Brown (siderite), yellow (calcite), and grey (limestone)
Luster: Waxy to dull

Identified May 10, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed during the Cretaceous period (50-70 million years ago) when volcanic eruptions killed sea life that sank to the ocean floor. Decomposing organic matter caused minerals to accumulate into nodules. As they dried, they cracked, and calcite/siderite filled the veins.

Uses & applications

Primarily used for decorative carvings, lapidary arts, jewelry, and as metaphysical or collector specimens. Not suitable for heavy construction due to varied hardness.

Geological facts

The name comes from the Latin word 'septum', meaning partition, referring to the cracks that divide the nodule. They are colloquially known as Dragon Stones because the pattern resembles dragon scales.

Field identification & locations

Identify in the field by looking for rounded, heavy concretions in shale or clay deposits. Often found in Utah, USA and Madagascar. When cracked open, they reveal distinctive yellow-centered internal patterns.

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