sedimentary
Chert (River Pebble)
Microcrystalline silica (SiO2)
Hardness: 7 on Mohs scale; Color: Gray with yellowish-brown iron staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Gray with yellowish-brown iron staining
- Luster
- Waxy to dull
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 on Mohs scale; Color: Gray with yellowish-brown iron staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed from the precipitation of silica from seawater or groundwater, often replacing organic material or carbonate. This specimen is a water-worn river pebble, likely shaped over thousands of years by fluvial erosion.
Uses & applications
Historically used for stone tools and arrowheads due to its sharp edges; currently used as construction aggregate, road base, and occasionally for lapidary tumbling.
Geological facts
Chert was one of the most important minerals for early human survival, used globally for flint-knapping into tools and fire-starting (flint is a high-purity variety of chert).
Field identification & locations
Identify by its hardness (will scratch glass), smooth texture, and waxy luster. Look for it in riverbeds, glacial deposits, or embedded in limestone outcrops.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
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
sedimentary