sedimentary

Ferruginous Sandstone (Ironstone)

Ferruginous arenite

AI-generated identification · may be incorrect

Hardness: 6-7 (Mohs); Color: Dark brown, reddish-brown, or rusty; Luster: Dull/Earthy; Structure: Clastic, fine to medium-grained; Cleavage: None; Specific Gravity: 2.5-3.0

Hardness: 6-7 (Mohs)
Color: Dark brown, reddish-brown, or rusty
Luster: Dull/Earthy

Identified July 15, 2026More sedimentary →

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Physical properties

Hardness: 6-7 (Mohs); Color: Dark brown, reddish-brown, or rusty; Luster: Dull/Earthy; Structure: Clastic, fine to medium-grained; Cleavage: None; Specific Gravity: 2.5-3.0

Formation & geological history

Formed through the lithification of sand grains where iron oxides (like hematite or goethite) act as the primary cementing agent. Often found in ancient riverbeds or marine environments.

Uses & applications

Used as a construction material, an iron ore source in historical times, and for architectural stone. Collectors value unusual weathering patterns.

Geological facts

This rock gets its dark color from the oxidation of iron. In desert environments, these rocks often develop a 'desert varnish' which makes them appear almost black or metallic.

Field identification & locations

Identify by its heavy weight (due to iron content), grainy texture, and distinctive reddish-brown streak. Common in arid regions or areas with high iron-rich groundwater.