sedimentary
Sandstone (Red Arkose)
Sandstone (Arkose variant, primarily SiO2 with KAlSi3O8)
Hardness: 6-7 (Mohs scale); Color: Reddish-brown, tan, or rusty orange; Luster: Dull/Earthy; Crystal structure: Clastic (composed of mineral grains); Cleavage: None (grains are cemented); Specific gravity: 2.2 - 2.8
- Hardness
- 6-7 (Mohs scale)
- Color
- Reddish-brown, tan, or rusty orange
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Reddish-brown, tan, or rusty orange; Luster: Dull/Earthy; Crystal structure: Clastic (composed of mineral grains); Cleavage: None (grains are cemented); Specific gravity: 2.2 - 2.8
Formation & geological history
Formed through the accumulation and cementation of mineral grains or rock fragments. Red coloring indicates iron oxide (hematite) cementation. Usually formed in terrestrial environments like riverbeds or deserts during periods of high erosion of granitic mountains.
Uses & applications
Commonly used as a building material, paving stone, and in the manufacturing of glass. Well-formed specimens are used by collectors to study sedimentary environments.
Geological facts
Red sandstone is what gives famous landmarks like the Grand Canyon and Australian Uluru (Ayers Rock) their distinct colors. It often preserves ripple marks and cross-bedding from ancient water currents.
Field identification & locations
Identify in the field by its gritty, sandpaper-to-the-touch texture and visible layers (bedding). It is found globally in sedimentary basins. Collectors should look for unique rounding (cobbles) or fossil inclusions.
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