sedimentary
Ferruginous Sandstone (Red Sandstone)
Arenite with Hematite/Limonite cement
Hardness: 6-7 (Mohs scale); Color: Earthy red, brown, tan; Luster: Dull/Earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific gravity: 2.2-2.8
- Hardness
- 6-7 (Mohs scale)
- Color
- Earthy red, brown, tan
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Earthy red, brown, tan; Luster: Dull/Earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific gravity: 2.2-2.8
Formation & geological history
Formed through the accumulation and cementation of sand-sized mineral grains, primarily quartz. The red and brown hues indicate oxidative weathering where iron-rich minerals like hematite or goethite coat the sand grains. Common in terrestrial environments like deserts or riverbeds.
Uses & applications
Used primarily in building construction as flagstone, decorative landscaping, and occasionally as a source of iron if the concentration is exceptionally high. Historical use in 'brownstone' architecture.
Geological facts
Many of the world's most famous natural landscapes, such as the Grand Canyon and the Australian Outback, owe their vibrant red colors to this type of iron-rich sedimentary rock.
Field identification & locations
Identify in the field by its gritty, sandpaper-like texture and its distinct layering (bedding). It will not fizz with acid unless it has calcite cement. Commonly found in arid regions and basins.
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