sedimentary

Septarian Nodule (Pebble)

Septarian concretion (composition: CaCO3, calcite, aragonite, and clay/mudstone)

Hardness: 3.5-4.0; Color: Earthy tan/grey exterior with dark grey or brown mineral-filled cracks; Luster: Dull (exterior) to vitreous (veins); Texture: Smooth, rounded water-worn pebble surface showing internal shrinkage patterns.

Hardness: 3
Luster: Dull (exterior) to vitreous (veins)

Identified July 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed during the Cretaceous period (approx. 50-70 million years ago) when mud balls in ancient sea beds dried and cracked. These cracks were later filled with minerals like calcite or aragonite precipitating from groundwater.

Uses & applications

Commonly used as lapidary material, decorative display pieces, wellness stones, and educational geological specimens.

Geological facts

Also known as 'Dragon Stones', the name 'septarian' comes from the Latin word 'septum', meaning partition, referring to the cracks that divide the nodule. The dark lines on this pebble are the 'septaria' veins visible on the surface due to river or beach erosion.

Field identification & locations

Identify by the distinctive 'cracked' or 'web-like' pattern of darker mineral veins against a lighter matrix. Frequently found in areas with sedimentary shale, such as Utah (USA), Madagascar, and various coastal riverbeds.

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