sedimentary
River Siltstone Pebble
Siltstone (primarily composed of silica and clay minerals)
Hardness: 3-6 Mohs; Color: Gray, tan, or greenish-gray; Luster: Dull/Earthy; Crystal Structure: Clastic (non-visible crystals); Cleavage: None/Irregular; Specific Gravity: 2.3-2.6
- Hardness
- 3-6 Mohs
- Color
- Gray, tan, or greenish-gray
- Luster
- Dull/Earthy
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 3-6 Mohs; Color: Gray, tan, or greenish-gray; Luster: Dull/Earthy; Crystal Structure: Clastic (non-visible crystals); Cleavage: None/Irregular; Specific Gravity: 2.3-2.6
Formation & geological history
Formed through the accumulation and litification of silt-sized particles. This specimen appears water-worn, smoothed by transport in a river or coastal environment over thousands of years.
Uses & applications
Used primarily in construction as fill material or aggregate. Smooth river stones are popular in decorative landscaping and aquarium decor.
Geological facts
Siltstone is intermediate between sandstone and shale. While it looks like a simple rock, layered siltstone can often contain microscopic fossils or impressions of ripple marks from ancient riverbeds.
Field identification & locations
Identify in the field by its smooth, rounded texture (if river-worn) and lack of visible grains compared to sandstone. It feels slightly grittier than shale but smoother than sandstone. Commonly found in riverbeds and glacial deposits.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary