sedimentary

Concretion with Quartz Veining

Septarian Concretion (CaCO3 / SiO2)

Hardness: 3-4 (matrix) to 7 (veins). Color: Tan, grey, white. Luster: Dull matrix with vitreous veins. Structure: Massively microcrystalline with crystalline fractures. Cleavage: None. Specific Gravity: 2.6-2.8.

Hardness: 3-4 (matrix) to 7 (veins)
Color: Tan, grey, white
Luster: Dull matrix with vitreous veins

Identified May 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of mineral cement within the spaces between particles in sedimentary layers, often during the Jurassic or Cretaceous periods. The cracks (septaria) formed through shrinkage and were later filled by calcite or quartz.

Uses & applications

Primarily used as decorative display pieces, garden ornaments, or for educational geological collections. Polished sections are often sold in rock shops.

Geological facts

These are often mistaken for dinosaur eggs due to their rounded shape and internal patterns. The name 'Septarian' comes from the Latin 'septum' meaning partition, referring to the cracks that divide the concretion.

Field identification & locations

Identify by the distinctive network of protruding veins (ribbing) on a rounded, weathered surface. Commonly found in coastal erosion zones or sedimentary basins such as in Utah, Michigan, or the UK.

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