sedimentary

Septarian Nodule

Septarian concretion (Complex mixture of Siderite/Limestone, Calcite, and Aragonite)

Hardness: 3.5-4 (Mohs scale); Color: Brown, tan, and grey with yellow to white veins; Luster: Earthy to vitreous in veins; Texture: Crystalline veins within a fine-grained matrix; Cleavage: None for the rock, rhombohedral for calcite infill.

Hardness: 3
Color: Brown, tan, and grey with yellow to white veins
Luster: Earthy to vitreous in veins

Identified April 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as mud balls in ancient sea beds during the Cretaceous period (50-70 million years ago); they dried and cracked, and the cracks were later filled with mineral precipitates like calcite and aragonite.

Uses & applications

Primarily used for decorative purposes, collecting, jewelry (cabochons), and as museum display specimens. Highly prized for their 'dragon skin' appearance.

Geological facts

Also known as 'Dragon Stones'; they are famous for their unique internal patterns that never repeat. Large nodules can reach several feet in diameter.

Field identification & locations

Identify by the pattern of angular cracks or veins (septaria) on the surface or inside. Commonly found in Utah, USA (the 'Muddy Creek' area) and Madagascar. Collectors look for high contrast between the matrix and the crystals.

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