sedimentary
Red Siltstone
Siltstone (primarily quartz and feldspar sized 0.0039 to 0.0625 mm)
Hardness: 3-4 (Mohs); Color: Reddish-brown due to iron oxide (hematite); Luster: Dull/Earthy; Crystal structure: Clastic (microcrystalline quartz); Cleavage: None/Planar bedding; Specific gravity: 2.6
- Hardness
- 3-4 (Mohs)
- Color
- Reddish-brown due to iron oxide (hematite)
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3-4 (Mohs); Color: Reddish-brown due to iron oxide (hematite); Luster: Dull/Earthy; Crystal structure: Clastic (microcrystalline quartz); Cleavage: None/Planar bedding; Specific gravity: 2.6
Formation & geological history
Formed by the deposition and lithification of silt-sized particles in low-energy aquatic environments like floodplains, lake beds, or marine shelves. Often represents geological periods like the Devonian or Triassic.
Uses & applications
Used primarily as low-grade fill in construction, aggregate for road bases, and occasionally as decorative garden stones or rustic interior flagstones.
Geological facts
Siltstones are midway between sandstones and shales; they are distinguished from shales by their lack of fissility (the ability to split into thin layers). The red color indicates oxygen was present during formation.
Field identification & locations
Identify in the field by its fine-grained texture (gritty to the teeth but smooth to the touch) and lack of visible grains. It is commonly found in sedimentary basins worldwide.
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