sedimentary
Sandstone (Ferruginous)
Sandstone (mainly SiO2 with Fe2O3 staining)
Hardness: 6-7 on Mohs scale (for grains); Color: Reddish-brown to tan; Luster: Dull/Earthy; Crystal structure: Clastic (sand-sized grains); Cleavage: None (granular); Specific Gravity: 2.2-2.8
- Hardness
- 6-7 on Mohs scale (for grains)
- Color
- Reddish-brown to tan
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 on Mohs scale (for grains); Color: Reddish-brown to tan; Luster: Dull/Earthy; Crystal structure: Clastic (sand-sized grains); Cleavage: None (granular); Specific Gravity: 2.2-2.8
Formation & geological history
Formed through the accumulation and cementation of mineral particles or rock fragments (clastic material). The reddish color is due to iron oxide (hematite) staining of the silica grains during diagenesis in oxygen-rich environments.
Uses & applications
Commonly used in construction as a building stone or paving material. Crushed sandstone is used in road bases. Finely grained varieties are used for grindstones and glass making.
Geological facts
Sandstone makes up about 20% of all sedimentary rocks on Earth. The famous 'Red Rocks' of the American Southwest are primarily ferruginous sandstones. It is often a key reservoir rock for petroleum and groundwater.
Field identification & locations
Identify by its gritty texture (feels like sandpaper) and visible sand grains. Look for layering (bedding) and test hardness (grains will scratch glass if quartz-based). Commonly found in river beds, deserts, and coastal areas.
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