sedimentary
Sandstone (Ferruginous / River-worn Cobble)
Sandstone (SiO2 with iron oxide impurities)
Hardness: 6-7 on Mohs scale. Color: Grayish-tan to reddish-brown due to iron oxide staining. Luster: Dull to earthy. Texture: Medium-grained, granular, rounded and smoothed by river erosion.
- Hardness
- 6-7 on Mohs scale
- Color
- Grayish-tan to reddish-brown due to iron oxide staining
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Grayish-tan to reddish-brown due to iron oxide staining. Luster: Dull to earthy. Texture: Medium-grained, granular, rounded and smoothed by river erosion.
Formation & geological history
Formed by the compaction and cementation of sand-sized mineral particles or rock fragments in deltaic, riverbed, or desert environments. Over time, water action smoothed and rounded the cobble.
Uses & applications
Commonly used as construction aggregate, paving stone, landscaping material, and for general geological study.
Geological facts
Sandstone makes up about 20% of all sedimentary rocks on Earth. The reddish or brownish hues are caused by iron oxide (hematite or goethite) acting as a natural cement or surface stain.
Field identification & locations
Identified in the field by its gritty surface texture (feels like sandpaper) and visible layering or color staining. Widely found in riverbeds, canyons, and sedimentary basins globally.
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