sedimentary
Chert (with Iron Staining)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: typically gray, green, or brown (often with red/orange iron oxidation); Luster: waxy to dull; Structure: microcrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- 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: typically gray, green, or brown (often with red/orange iron oxidation); Luster: waxy to dull; Structure: microcrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the precipitation of silica from seawater or the replacement of limestone by silica-rich fluids. Often contains the remains of microscopic organisms like diatoms or radiolarians. Found in sedimentary deposits of various geological ages.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its conchoidal fracture. Today used in construction aggregate, road surfacing, and as a collector's specimen.
Geological facts
Chert was one of the most important minerals for early humans because its sharp edges were ideal for cutting and hunting. When struck against steel, it can produce sparks, used for thousands of years to start fires.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, glass-like (conchoidal) fracture surfaces. Common in river beds and limestone outcrops.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary