sedimentary
Siltstone Pebble
Siltstone (fine-grained siliciclastic sedimentary rock)
Hardness: 6-7 (Mohs); Color: Tan to light brown; Luster: Dull/Earthy; Crystal structure: Non-crystalline visible grain; Cleavage: None; Specific Gravity: 2.3-2.6
- Hardness
- 6-7 (Mohs)
- Color
- Tan to light brown
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Tan to light brown; Luster: Dull/Earthy; Crystal structure: Non-crystalline visible grain; Cleavage: None; Specific Gravity: 2.3-2.6
Formation & geological history
Formed through the accumulation and lithification of silt-sized particles (larger than clay, smaller than sand) in low-energy aquatic environments like lake beds or floodplains. Most accessible specimens are from the Paleozoic to Cenozoic eras.
Uses & applications
Used primarily as fill material in construction, as a component of cement, or as decorative river rock in landscaping.
Geological facts
Siltstone is often mistaken for shale, but it lacks the 'fissility' (tendency to split into layers) that shale possesses. This specific specimen has been rounded by fluvial (water) erosion.
Field identification & locations
Identify in the field by its smooth feel compared to sandstone but grittier feel compared to claystone; it will not scratch easily with a fingernail. Commonly found in riverbeds and coastal areas.
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