sedimentary
Sandstone (specifically Arkose or Quartz Arenite)
Arenite (primarily SiO2 with possible Feldspar)
Hardness: 6-7 on Mohs scale (depending on cementation); Color: Tan, brown, or reddish-brown; Luster: Dull/Earthy; Crystal structure: Clastic (sand grains); Cleavage: None; Specific gravity: 2.2–2.8. Highly visible horizontal bedding planes (lamination).
- Hardness
- 6-7 on Mohs scale (depending on cementation)
- Color
- Tan, brown, or reddish-brown
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 on Mohs scale (depending on cementation); Color: Tan, brown, or reddish-brown; Luster: Dull/Earthy; Crystal structure: Clastic (sand grains); Cleavage: None; Specific gravity: 2.2–2.8. Highly visible horizontal bedding planes (lamination).
Formation & geological history
Formed by the accumulation and lithification of sand-sized mineral grains or rock fragments. The distinct layers visible in the specimen indicate deposition in a high-energy environment like a riverbed, beach, or desert dune over thousands to millions of years.
Uses & applications
Used extensively as a construction materials (building stone), in the manufacture of glass (if high purity quartz), and as an abrasive in grinding wheels. It is also an important reservoir rock for groundwater, oil, and natural gas.
Geological facts
Sandstone accounts for roughly 20-25% of all sedimentary rocks in the Earth's crust. Famous structures like the treasury at Petra and many of the early American 'Brownstone' buildings are made from variations of this rock.
Field identification & locations
Identify in the field by its 'sandpaper' feel and visible horizontal layering (bedding). It is found worldwide in sedimentary basins. Collectors should look for cross-bedding or ripple marks which can indicate the flow direction of ancient water systems.
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