sedimentary
Ferruginous Sandstone
Iron-rich Clastic Sedimentary Rock
Hardness: 6-7 (Mohs); Color: Dark brown, reddish-brown, grey; Luster: Dull to earthy; Structure: Granular, fine-to-medium grained; Cleavage: None; Specific Gravity: 2.3-2.8
- Hardness
- 6-7 (Mohs)
- Color
- Dark brown, reddish-brown, grey
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark brown, reddish-brown, grey; Luster: Dull to earthy; Structure: Granular, fine-to-medium grained; Cleavage: None; Specific Gravity: 2.3-2.8
Formation & geological history
Formed through the accumulation and cementation of sand-sized mineral grains or rock fragments, within which iron oxides (hematite or goethite) act as the primary cementing agent. Often found in ancient riverbeds or coastal environments.
Uses & applications
Commonly used as a building stone or road aggregate; historically used in some regions as a low-grade iron ore.
Geological facts
The reddish-brown staining is known as 'desert varnish' when it appears as a thin coating, though here it appears deeply integrated into the matrix. It is extremely common in the Triassic-age basins of the eastern United States.
Field identification & locations
Identify by its gritty sandpaper-like texture and the presence of deep brown or orange-red oxidation. It is frequently found in weathered outcrops or as river cobbles. Collectors look for unique weathering patterns or fossils within the layers.
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