sedimentary

Ironstone Concretion

Siderite or Hematite Concretion (FeCO3 or Fe2O3)

AI-generated identification · may be incorrect

Hardness: 4-6 on Mohs scale; Color: Rusty brown, tan, or dark red; Luster: Dull to earthy; Structure: Concentric layering (liesegang rings); Cleavage: None; Specific Gravity: 3.0-4.0

Hardness: 4-6 on Mohs scale
Color: Rusty brown, tan, or dark red
Luster: Dull to earthy

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 4-6 on Mohs scale; Color: Rusty brown, tan, or dark red; Luster: Dull to earthy; Structure: Concentric layering (liesegang rings); Cleavage: None; Specific Gravity: 3.0-4.0

Formation & geological history

Formed by the precipitation of mineral cement within the spaces between sediment grains, often around a nucleus like a leaf or shell. These typically form in sedimentary basins over millions of years.

Uses & applications

Historically used as a low-grade iron ore; commonly collected as geological curiosities or used in landscaping and garden decoration.

Geological facts

Small, round ironstone concretions found on Mars are nicknamed 'blueberries,' providing evidence of past water on the planet. On Earth, they are often mistaken for fossils or meteorites due to their unusual shapes.

Field identification & locations

Identify in the field by looking for rounded or 'pill-shaped' nodules that are significantly heavier and harder than the surrounding sandstone or shale. They often exhibit 'onion-skin' weathering layers.