sedimentary

River Siltstone Pebble

Siltstone (primarily composed of silica and clay minerals)

AI-generated identification · may be incorrect

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 April 13, 2026More sedimentary →

Explore River Siltstone Pebble in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

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.