sedimentary
Ocherous Sandstone (Ferruginous Sandstone)
Ferruginous Arenite (SiO2 with Fe2O3)
Hardness: 6-7 (Mohs scale); Color: Reddish-brown, orange, tan; Luster: Dull, earthy; Crystal structure: Clastic (granular); Cleavage: None (conchoidal to uneven fracture); Specific gravity: 2.2-2.8
- Hardness
- 6-7 (Mohs scale)
- Color
- Reddish-brown, orange, tan
- Luster
- Dull, earthy
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Reddish-brown, orange, tan; Luster: Dull, earthy; Crystal structure: Clastic (granular); Cleavage: None (conchoidal to uneven fracture); Specific gravity: 2.2-2.8
Formation & geological history
Formed by the accumulation and cementation of sand-sized grains, typically quartz, where iron oxide (hematite or limonite) acts as the cementing agent. These deposits often date from the Paleozoic to Mesozoic eras in ancient riverbeds or marine environments.
Uses & applications
Used in construction as building stone, road base, and crushed aggregate. Historically used as a pigment (ochre) for paints and dyes. High-purity sandstones are used in glass manufacturing.
Geological facts
The red color is caused by the oxidation of iron, a process similar to rusting. This type of rock is responsible for the dramatic landscapes in places like the Red Rocks Amphitheatre and the Grand Canyon.
Field identification & locations
Identify in the field by its gritty, sandpaper-like texture and visible layers (bedding). It will not fizz with acid (distinguishing it from limestone). Commonly found in sedimentary basins and arid environments worldwide.
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