sedimentary

Septarian Nodule

Septarian concretion (Calcium Carbonate, Aragonite, and Siderite/Baryte)

Hardness: 3.5 to 4.0; Color: Brown, yellowish, gray, and black; Luster: Waxy to dull (earthy); Structure: Microcrystalline with distinct shrinkage cracks; Cleavage: Perfect rhombohedral in calcite areas.

Hardness: 3
Color: Brown, yellowish, gray, and black
Luster: Waxy to dull (earthy)

Identified July 10, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed during the Cretaceous Period (50-70 million years ago) in marine environments. Volcanic eruptions killed sea life which sank to the seafloor; as it decomposed, minerals formed a nodule. As the oceans receded, the nodules dried out and cracked, later filling with calcite or aragonite.

Uses & applications

Primarily used for ornamental purposes, lapidary work, jewelry (cabochons), and as display specimens for collectors.

Geological facts

The name 'Septarian' comes from the Latin word 'septum', meaning partition or wall, referring to the cracks that divide the nodule. They are sometimes called 'Dragon Stones' in folklore.

Field identification & locations

Identify by the characteristic 'tortoise shell' pattern of cracks filled with crystalline minerals. Found commonly in Utah (USA), Madagascar, and the UK. Collectors should look for nodules in clay-rich sedimentary layers.

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