sedimentary
Sandstone (Ferruginous)
Arenite with Iron Oxide cement (primarily SiO2 with Fe2O3)
Hardness: 6-7 (Mohs); Color: Reddish-brown to tan; Luster: Dull/Earthly; Crystal structure: Granular/Clastic; Cleavage: None; Specific Gravity: 2.2–2.8
- Hardness
- 6-7 (Mohs)
- Color
- Reddish-brown to tan
- Luster
- Dull/Earthly
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Physical properties
Hardness: 6-7 (Mohs); Color: Reddish-brown to tan; Luster: Dull/Earthly; Crystal structure: Granular/Clastic; Cleavage: None; Specific Gravity: 2.2–2.8
Formation & geological history
Formed from the mechanical weathering of pre-existing rocks and the deposition of sand-sized grains in environments such as rivers, deserts, or beaches. The iron oxide (rust) acts as a cementing agent, giving it the characteristic brown color.
Uses & applications
Commonly used as a building material, in paving, for decorative landscaping, and as an aquifer in geology due to its porosity.
Geological facts
Sandstone makes up approximately 20-25% of all sedimentary rocks on Earth. The famous red rocks of the Grand Canyon and Petra in Jordan are primarily made of ferruginous sandstone.
Field identification & locations
Identify in the field by its gritty texture (feels like sandpaper) and visible sand grains. Look for layering (bedding). Found worldwide in sedimentary basins; collectors look for specimens with unique ripple marks or fossil inclusions.
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