sedimentary

Ironstone Concretions (Ironstone)

Ferruginous Sandstone or Siltstone (Fe2O3)

AI-generated identification · may be incorrect

Hardness: 5-6 (Mohs scale), Color: Dark brown, reddish-brown, or blackish, Luster: Dull to sub-metallic, Structure: Amorphous or microcrystalline, Cleavage: None, SG: 3.0-4.5

Identified February 19, 2026More sedimentary →

Explore Ironstone Concretions (Ironstone) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 5-6 (Mohs scale), Color: Dark brown, reddish-brown, or blackish, Luster: Dull to sub-metallic, Structure: Amorphous or microcrystalline, Cleavage: None, SG: 3.0-4.5

Formation & geological history

Formed via the precipitation of iron-oxide minerals within sedimentary basins, typically when groundwater rich in mineral content reacts with sediment during diagenesis.

Uses & applications

Primary source of iron ore for smelting; also used as decorative gravel, in traditional pigments (ochre), and for historical construction in specific regions.

Geological facts

Often called 'Moqui Marbles' or 'Blueberry Rocks' when found in spherical shapes; similar iron-rich concretions have been discovered on Mars by the Opportunity rover.

Field identification & locations

Identify in the field by their extreme density compared to surrounding sandstone, rust-colored streak test, and often irregular, pitted, or smooth pebbled surfaces. Common in arid desert regions.