sedimentary

Ferruginous Sandstone (Gritstone)

Arenite with Iron-Oxide Cement (SiO2 with Fe2O3 and FeO(OH))

Hardness: 6-7 (Mohs scale); Color: Reddish-brown, rust, or tan; Luster: Dull/Earthy; Crystal Structure: Clastic (composed of rounded or angular sand grains); Cleavage: None; Specific Gravity: 2.2–2.8

Hardness: 6-7 (Mohs scale)
Color: Reddish-brown, rust, or tan
Luster: Dull/Earthy

Identified March 23, 2026More sedimentary →

Identify your own rocks.

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

App Store Google Play

Physical properties

Formation & geological history

Formed through the accumulation and compaction of sand-sized grains, primarily quartz, which are then cemented together by iron-oxide minerals (like hematite or goethite) precipitated from groundwater. Can range from Precambrian to Holocene in age.

Uses & applications

Used primarily in heavy construction, road aggregates, and as a dimension stone for rustic walls or landscaping. Historically used for millstones and sharpening tools.

Geological facts

The distinctive rusty color comes from the oxidation of iron minerals, essentially making this rock a naturally 'rusted' geological formation. It is common in arid environments and plateau regions.

Field identification & locations

Identify in the field by its sandpaper-like texture (clastic grains) and 'rusty' staining that may rub off slightly on hands. Commonly found in desert regions, ancient riverbeds, and cliff faces. Collectors look for unique banding or iron concretions.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Sandstone (Quartz-rich)

Arenite (SiO2)

sedimentary

Sandstone (with man-made markings)

Arenite (composed primarily of Quartz, SiO2)

sedimentary