sedimentary
Sandstone (Ferruginous)
Arenite (composed primarily of SiO2 with Fe2O3 cement)
Hardness: 6-7 (Mohs); Color: Reddish-brown, tan, or chocolate; Luster: Dull/Earthy; Crystal structure: Clastic (sand grains); Cleavage: None, breaks across grains; Specific gravity: 2.2-2.8
- Hardness
- 6-7 (Mohs)
- Color
- Reddish-brown, tan, or chocolate
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Reddish-brown, tan, or chocolate; Luster: Dull/Earthy; Crystal structure: Clastic (sand grains); Cleavage: None, breaks across grains; Specific gravity: 2.2-2.8
Formation & geological history
Formed by the accumulation of sand-sized grains of mineral or rock, which are then cemented together by minerals over millions of years. This specific dark color suggests iron-oxide (hematite or limonite) acting as the cementing agent in a terrestrial or desert environment.
Uses & applications
Used widely in construction (building blocks), as a source for sand in industrial processes, and as a decorative stone in landscaping.
Geological facts
Sandstone accounts for roughly 20% of all sedimentary rocks on Earth. The unique coloring of these rocks is often what gives famous landscapes, like the Grand Canyon or Sedona, their distinctive red and brown hues.
Field identification & locations
Identify in the field by its gritty 'sandpaper' feel and visible layers (bedding planes). When scratched with a knife, sand grains should fall off. Commonly found in riverbeds, cliffs, and desert basins.
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