sedimentary

Ironstone concretion / Limonitic Sandstone

Goethite/Hematite Cemented Sandstone (Hydrated Iron Oxide)

AI-generated identification · may be incorrect

Hardness: 5-5.5 (mohs); Color: Rusty brown, reddish-orange, tan; Luster: Dull/Earthy; Crystal Structure: Amorphous or Microcrystalline; Cleavage: None; Specific Gravity: 3.3-4.3

Hardness: 5-5
Color: Rusty brown, reddish-orange, tan
Luster: Dull/Earthy

Identified April 12, 2026More sedimentary →

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Physical properties

Hardness: 5-5.5 (mohs); Color: Rusty brown, reddish-orange, tan; Luster: Dull/Earthy; Crystal Structure: Amorphous or Microcrystalline; Cleavage: None; Specific Gravity: 3.3-4.3

Formation & geological history

Formed through the precipitation of iron-rich minerals (limonite, goethite) within the pore spaces of sedimentary sand. This usually occurs due to groundwater movement or oxidation in bog/wetland environments.

Uses & applications

Historically used as a low-grade iron ore (bog iron). Currently used as landscaping stone, natural pigments (ochre), or as a curiosity/educational specimen for amateur collectors.

Geological facts

These are often mistaken for meteorites or fossils (like coprolites) due to their unusual organic shapes and heavy weight. They can form around a nucleus of organic matter like a leaf or shell.

Field identification & locations

Identify by its 'rusty' appearance and relatively high weight compared to normal sandstone. Commonly found in areas with high iron content in groundwater or exposed sedimentary beds. It will leave a yellow-brown streak on a porcelain plate.