sedimentary
Red Siltstone
Siltstone (composed of Quartz and Clay minerals)
Hardness: 6-7 on Mohs scale; Color: Reddish-brown to maroon; Luster: Dull/Earthy; Structure: Clastic; Cleavage: None (conchoidal fracture when fine-grained); Specific Gravity: 2.6
- Hardness
- 6-7 on Mohs scale
- Color
- Reddish-brown to maroon
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Reddish-brown to maroon; Luster: Dull/Earthy; Structure: Clastic; Cleavage: None (conchoidal fracture when fine-grained); Specific Gravity: 2.6
Formation & geological history
Formed through the accumulation and compaction of silt-sized particles in low-energy environments like lake beds or river floodplains. The red color suggests deposition in an oxidizing environment where iron-rich minerals rusted.
Uses & applications
Commonly used as fill material in construction, for landscaping, and occasionally as a source of quartz if pure enough.
Geological facts
Siltstone is intermediate between sandstone and shale. The presence of fine white/greenish veins suggests secondary mineralization, often quartz or calcite, filling old fractures.
Field identification & locations
Identify by its gritty feel (finer than sandstone) and lack of distinct fissility compared to shale. Often found in riverbeds or eroded sedimentary basins.
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