sedimentary

Septarian Nodule Segment (Turtle Stone)

Septarian Concretion (CaCO3 with Siderite or Calcite infill)

AI-generated identification · may be incorrect

Hardness: 3.5-4.0 (Mohs scale); Color: Creamy grey to tan exterior with tan/brown cracks; Luster: Dull/earthy exterior; Structure: Microcrystalline with distinct angular shrinkage cracks (septaria).

Hardness: 3
Color: Creamy grey to tan exterior with tan/brown cracks
Luster: Dull/earthy exterior

Identified March 20, 2026More sedimentary →

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Physical properties

Hardness: 3.5-4.0 (Mohs scale); Color: Creamy grey to tan exterior with tan/brown cracks; Luster: Dull/earthy exterior; Structure: Microcrystalline with distinct angular shrinkage cracks (septaria).

Formation & geological history

Formed during the Cretaceous period (approx. 50-70 million years ago) in marine environments. They began as mud balls that cracked as they dehydrated; mineral-rich water then filled the cracks with calcite or siderite.

Uses & applications

Used primarily as decorative specimens, lapidary material for cabochons, and unique collector pieces. Large nodules are often sliced and polished for display.

Geological facts

Also known as 'Dragon Stones' or 'Turtle Stones' due to the shell-like pattern created by the cracks. They are common in areas that were once prehistoric seafloors.

Field identification & locations

Identify in the field by the distinct 'network' of raised or recessed cracks on a rounded, heavy stone. Commonly found in Utah (USA), Madagascar, and various dry lake beds or coastal cliffs. Collectors should look for nodules with high contrast between the host rock and the vein fill.