sedimentary

Septarian Nodule or Mud Crack Fossil

Septarian Nodule (Concretion)

AI-generated identification · may be incorrect

Hardness: 3.5-4.0 (for calcite centers); Color: Brown, tan, cream, and grey; Luster: Waxy to dull (earthy); Structure: Massive/Crystalline infilling; Cleavage: None/Conchoidal.

Hardness: 3
Color: Brown, tan, cream, and grey
Luster: Waxy to dull (earthy)

Identified April 6, 2026More sedimentary →

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Physical properties

Hardness: 3.5-4.0 (for calcite centers); Color: Brown, tan, cream, and grey; Luster: Waxy to dull (earthy); Structure: Massive/Crystalline infilling; Cleavage: None/Conchoidal.

Formation & geological history

Formed during the Cretaceous period (50-70 million years ago) from mud balls and organic matter in ancient seabeds. As the mud dried and shrank, cracks formed and were later filled with minerals like calcite and aragonite via groundwater infiltration.

Uses & applications

Used primarily for home decor, lapidary items (bookends, spheres), jewelry, and as educational geological specimens for collectors.

Geological facts

Also known as 'Dragon Stones' due to their scaly appearance. They represent a rare combination of mineral formation and shrinkage-crack patterns that preserve a specific moment in the chemical history of an ancient seafloor.

Field identification & locations

Identify by the angular 'lightning' patterns or cracks separating dark brown mudstone areas from lighter crystalline centers. Commonly found in Utah, Madagascar, and Morocco.