sedimentary

Septarian Nodule

Septarian Concretion (CaCO3, CaMg(CO3)2, SiO2)

Hardness: 3-4 (Calcite parts) to 7 (Aragonite/Quartz); Color: Gray or brown exterior with yellow calcite, brown aragonite, and clear quartz centers; Luster: Dull or earthy exterior, vitreous to waxy interior; Structure: Microcrystalline with distinct internal shrinkage cracks (septaria).

Hardness: 3-4 (Calcite parts) to 7 (Aragonite/Quartz)
Luster: Dull or earthy exterior, vitreous to waxy interior

Identified May 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed during the Cretaceous period (approx. 50-70 million years ago). They originated as mud balls on ancient sea floors, which hardened and cracked due to dehydration and volcanic activity, later filling with minerals like calcite and aragonite.

Uses & applications

Primarily used for decorative purposes, lapidary work (cabochons), interior design items like bookends and bowls, and as educational geological specimens.

Geological facts

Also known as 'Dragon Stones' due to their cracked, scaly appearance. They are unique because they are a combination of different minerals that formed at different times within a single sedimentary structure.

Field identification & locations

Identify by the distinctive 'cracked' pattern (septaria) visible when the rock is broken or cut. Commonly found in Utah (USA), Madagascar, and parts of the UK. Collectors look for high contrast colored patterns.

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Brecciated Chert (Microcrystalline Silica)

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Sandstone (Quartz-rich)

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