sedimentary
Sandstone (Ferruginous)
Arenite with Iron-Oxide Cement
Hardness: 6-7 (Mohs scale); Color: Brown, reddish-brown, tan; Luster: Dull to earthy; Crystal structure: Clastic (grainy texture); Cleavage: None; Specific gravity: 2.2-2.8.
- Hardness
- 6-7 (Mohs scale)
- Color
- Brown, reddish-brown, tan
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Brown, reddish-brown, tan; Luster: Dull to earthy; Crystal structure: Clastic (grainy texture); Cleavage: None; Specific gravity: 2.2-2.8.
Formation & geological history
Formed by the accumulation and cementation of sand-sized silicate grains (mostly quartz). The dark reddish-brown color indicates 'ferruginous' sandstone, where iron oxide (hematite or limonite) acts as the cementing agent. These typically form in terrestrial arid environments or river beds.
Uses & applications
Used primarily as a building material, paving stone, and in glass manufacturing or metal casting if high in silica. Iron-rich varieties are occasionally used for landscaping.
Geological facts
Sandstone makes up about 20% of all sedimentary rocks on Earth. This specific variety's color is the same chemistry that gives the planet Mars its reddish hue.
Field identification & locations
Identify in the field by its sandpaper-like feel and visible grain structure. It often forms prominent cliffs or flat-topped mesas in desert regions.
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