sedimentary
Flesh-toned Siltstone
Siltstone (composed of microscopic Quartz and Feldspar grains)
Hardness: 3-4 (Mohs scale); Color: Pale pinkish-tan to peach; Luster: Dull/Earthy; Crystal Structure: Clastic (non-crystalline appearance); Cleavage: None; Specific Gravity: 2.6 - 2.7
- Hardness
- 3-4 (Mohs scale)
- Color
- Pale pinkish-tan to peach
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3-4 (Mohs scale); Color: Pale pinkish-tan to peach; Luster: Dull/Earthy; Crystal Structure: Clastic (non-crystalline appearance); Cleavage: None; Specific Gravity: 2.6 - 2.7
Formation & geological history
Formed by the accumulation and lithification of silt-sized particles (0.0039 to 0.0625 mm). These sediments typically settle in low-energy environments like river floodplains, lagoons, or deep-water basins. This specimen appears consistent with fine-grained Permian or Triassic 'Red Bed' deposits.
Uses & applications
Used primarily in construction as fill material or as a base for roads. High-quality varieties are sometimes used for flagstone or interior decorative tiles. In industry, it can be a source of ground silica.
Geological facts
Siltstone is often mistaken for shale, but it lacks the characteristic fissility (capability of being split into thin sheets). It feels gritty against the teeth, unlike clay-rich shale which feels smooth.
Field identification & locations
Identify in the field by its fine grain size (visible only under high magnification) and 'gritty' feel compared to mudstone. Common in sedimentary basins worldwide. For collectors, look for specimens with ripple marks or trace fossils.
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