sedimentary
Siltstone
Siltstone
Hardness: 3-4 (Mohs); Color: Grey, brown, or reddish-brown; Luster: Dull/Earthy; Crystal structure: Non-crystalline clastic; Cleavage: None, can show fissility; Specific gravity: 2.3-2.6
- Hardness
- 3-4 (Mohs)
- Color
- Grey, brown, or reddish-brown
- Luster
- Dull/Earthy
Identified More sedimentary →
Explore Siltstone in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 3-4 (Mohs); Color: Grey, brown, or reddish-brown; Luster: Dull/Earthy; Crystal structure: Non-crystalline clastic; Cleavage: None, can show fissility; Specific gravity: 2.3-2.6
Formation & geological history
Formed through the lithification of silt-sized particles deposited in slow-moving water environments like floodplains, deltas, or lakes. Most specimens range from Paleozoic to Cenozoic eras.
Uses & applications
Used primarily as low-quality fill material in construction, as a source of soil minerals, and occasionally for decorative landscaping or flagstones if sufficiently durable.
Geological facts
Siltstone is intermediate between sandstone and shale; it has smaller grains than sandstone but lacks the extreme clay content and thin layering of true shale.
Field identification & locations
Identify by its gritty feel on teeth (unlike shale) but smooth appearance compared to sandstone. Commonly found in sedimentary basins and river outcrops.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary