sedimentary
Sandstone (Ferruginous)
Clastic sedimentary rock (primarily SiO2 with Fe2O3)
Hardness: 6-7 (Mohs scale); Color: Brown, reddish-brown, tan; Luster: Dull/Earthy; Structure: Clastic, fine-to-medium grained; Cleavage: None; Specific Gravity: 2.2-2.8
- Hardness
- 6-7 (Mohs scale)
- Color
- Brown, reddish-brown, tan
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Brown, reddish-brown, tan; Luster: Dull/Earthy; Structure: Clastic, fine-to-medium grained; 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 brown/red hue suggests iron-rich (ferruginous) cementation, often occurring in riverbeds, deserts, or coastal environments over millions of years.
Uses & applications
Commonly used as a building material, grit for sharpening, paving stones, and in the manufacturing of glass. Iron-rich varieties are occasionally studied for geochemical properties.
Geological facts
Sandstone makes up about 20% of all sedimentary rocks on Earth. The coloration is often due to hematite or goethite acting as a binding agent between quartz grains.
Field identification & locations
Identify by its gritty, sandpaper-like feel and visible pores. In the field, look for layering (bedding) and test the hardness; it should easily scratch glass if it is quartz-based.
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