sedimentary

Septarian Nodule or Concretion

Calcareous concretion with argillaceous and sideritic components

AI-generated identification · may be incorrect

Hardness: 3.5-4 (calcite), 7 (quartz if present); Color: Brown, yellow, gray, black; Luster: Dull to earthy (exterior), vitreous (calcite filled cracks); Crystal structure: Microcrystalline to macrocrystalline calcite in cracks; Cleavage: None visible in mass; Specific gravity: 2.6-2.9.

Hardness: 3
Color: Brown, yellow, gray, black
Luster: Dull to earthy (exterior), vitreous (calcite filled cracks)

Identified August 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine environments as sedimentary concretions around a nucleus (often organic). As the mud dried and shrank, cracks formed (septaria) which were later filled with minerals precipitating from groundwater, typically calcite, aragonite, or siderite. Usually Cretaceous or Jurassic in age.

Uses & applications

Often cut and polished for display, bookends, spheres, or ornamental use. Minor use in local landscaping or curiosity collecting.

Geological facts

The name 'septarian' comes from the Latin word 'septum', meaning partition, referring to the cracks and cavities within the nodule. They are sometimes called 'dragon stones' due to their scaly appearance when polished.

Field identification & locations

Identified by their rounded, nodular shape and the distinctive pattern of mineral-filled cracks on the surface or when broken/cut open. Commonly found in sedimentary rock formations, notably in Utah (USA), Madagascar, and parts of Europe. Look for them eroding out of shale or mudstone cliffs.