sedimentary
Ferruginous Sandstone
Sandstone with Iron Oxide (Limonite/Goethite)
Hardness: 6-7 (Mohs); Color: Rusty brown, ochre, or yellowish-orange; Luster: Dull or earthy; Crystal structure: Granular (clastic); Cleavage: None; Specific gravity: 2.3-2.6
- Hardness
- 6-7 (Mohs)
- Color
- Rusty brown, ochre, or yellowish-orange
- Luster
- Dull or earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Rusty brown, ochre, or yellowish-orange; Luster: Dull or earthy; Crystal structure: Granular (clastic); Cleavage: None; Specific gravity: 2.3-2.6
Formation & geological history
Formed through the lithification of sand grains where iron-rich groundwater precipitates iron oxides (like goethite or hematite) as a cementing agent between the quartz grains. Typically found in riverbeds, or as part of terrestrial sedimentary sequences.
Uses & applications
Mainly used as a building stone or road aggregate. Historically used as a low-grade iron ore in some regions. Highly valued as a rough landscape stone.
Geological facts
The distinct rusty color comes from the oxidation of iron minerals, essentially making this a 'rusted' rock. In some areas, these are called 'ironstones' if the iron content is high enough.
Field identification & locations
Identify by its gritty, sandpaper-like texture and its characteristic rusty staining that doesn't wash off. It is commonly found in sedimentary basins and along eroding cliffs or river banks.
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