sedimentary
Sandstone (Ferruginous)
Clastic Sedimentary Rock (SiO2 with FeO/Fe2O3)
Hardness: 6-7 (Mohs scale); Color: Brownish-red to tan; Luster: Dull/Earthy; Crystal structure: Clastic (sand grains); Cleavage: None; Specific gravity: 2.2–2.8
- Hardness
- 6-7 (Mohs scale)
- Color
- Brownish-red to tan
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Brownish-red to tan; Luster: Dull/Earthy; Crystal structure: Clastic (sand grains); Cleavage: None; Specific gravity: 2.2–2.8
Formation & geological history
Formed from the accumulation and cementation of sand-sized mineral grains or rock fragments. The reddish-brown color indicates iron-oxide cementation (limonite or hematite). Typically formed in river beds, beaches, or desert dunes over millions of years.
Uses & applications
Commonly used in construction, architectural stone, grindstones, and as a reservoir rock for water and petroleum.
Geological facts
Sandstone makes up about 10-20% of all sedimentary rocks on Earth. The 'red' sandstones of the American Southwest owe their color to the same iron oxidation process seen in this specimen.
Field identification & locations
Identify by its gritty texture (feels like sandpaper) and visible sand grains. Found globally in basins and near continental margins. For collectors, look for cross-bedding or fossil inclusions.
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