sedimentary
Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, and grey with iron staining; Luster: Waxy to dull (glassy when wet); Crystal Structure: Cryptocrystalline; Cleavage: None (conchoïdal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Brown, tan, and grey with iron staining
- Luster
- Waxy to dull (glassy when wet)
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, and grey with iron staining; Luster: Waxy to dull (glassy when wet); Crystal Structure: Cryptocrystalline; Cleavage: None (conchoïdal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed in marine environments through the accumulation of silica-rich microfossils or precipitation from silica-rich fluids. This specimen was secondary-weathered and rounded in a river or fluvial environment.
Uses & applications
Historically used for making stone tools (flintknapping); currently used as architectural aggregate, road surfacing, and as river rock for landscaping.
Geological facts
Chert has been used by humans for millions of years due to its ability to break with very sharp edges. It is chemically identical to quartz but has a different microscopic structure.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a steel knife), waxy appearance, and smooth, rounded surface if found in water. It is ubiquitous in riverbeds worldwide.
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