sedimentary
Sandstone (Ferruginous)
Ferruginous Sandstone (SiO2 with Fe2O3)
Hardness: 6-7 on Mohs scale; Color: Reddish-brown, tan, or ochre; Luster: Dull to earthy; Crystal Structure: Clastic (grains); Cleavage: None; Specific Gravity: 2.2-2.8.
- Hardness
- 6-7 on Mohs scale
- Color
- Reddish-brown, tan, or ochre
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Reddish-brown, tan, or ochre; Luster: Dull to earthy; Crystal Structure: Clastic (grains); Cleavage: None; Specific Gravity: 2.2-2.8.
Formation & geological history
Formed by the accumulation and cementation of sand-sized mineral grains or rock fragments. The reddish hue indicates iron oxide (hematite or limonite) acting as the cementing agent. Often associated with ancient riverbeds, deserts, or marine environments across various geological ages.
Uses & applications
Historically used as a construction material for buildings and monuments. In modern times, it is used for gravel, paving stones, or as a source of silica for glass manufacturing.
Geological facts
Sandstone represents about 20-25% of all sedimentary rocks on Earth. Ferruginous sandstone is specifically known for its distinct color which comes from the oxidation of iron minerals, similar to the process of rusting.
Field identification & locations
Identified by its gritty sandpaper-like texture and visible sand grains. Found globally in sedimentary basins. Collectors look for unique banding or patterns caused by mineral staining.
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