sedimentary

Tumbled septarian nodule fragment (probable)

Septarian calcite–aragonite concretion with brown clay/mudstone matrix

AI-generated identification · may be incorrect

Rounded, polished brown-gray specimen with a network of dark veins and pale cream infill. Likely hardness 3–4 overall (calcite veins: Mohs 3; aragonite: 3.5–4), earthy to waxy luster, fine-grained matrix, and irregular shrinkage fractures rather than crystal cleavage.

Identified September 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when carbonate-rich mud concretions dry and contract, producing polygonal cracks later filled by calcite or aragonite; commonly Cretaceous to Tertiary in age. Exact age and identity require testing because the image alone cannot confirm the mineral infill.

Uses & applications

Primarily a decorative and lapidary stone used for polished specimens, cabochons, carvings, and metaphysical collecting; it has little structural or industrial value.

Geological facts

The characteristic “crackled” pattern reflects desiccation and mineral-filled fractures, not fossil bones or ordinary surface cracks. Some nodules contain fossil fragments or hollow crystal-lined cavities.

Field identification & locations

Look for a heavy, opaque brown concretion with geometric vein networks; calcite veins fizz with dilute hydrochloric acid, while the matrix generally does not. Common sources include Madagascar, Utah, and Morocco.