sedimentary
Chert (and/or Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, brown with waxy luster; Crystal Structure: Microcrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, brown with waxy luster
Identified More sedimentary →
Explore Chert (and/or Flint) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, brown with waxy luster; Crystal Structure: Microcrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic debris (like diatom or radiolarian shells) or through chemical precipitation in marine environments. It often occurs as nodules or layers within limestone and chalk beds.
Uses & applications
Historically used for stone tools (arrowheads, knives) due to its sharp edges when fractured. Currently used as road surfacing material, in decorative landscaping, and occasionally for fire-starting (flint).
Geological facts
Chert was one of the most important minerals for early humans. Its ability to produce a predictable, razor-sharp edge made it the premier material for the Stone Age tool industry.
Field identification & locations
Identify in the field by its very smooth, waxy surface and its tendency to break with 'shell-like' (conchoidal) curves. It will easily scratch glass and will not react with acid. Commonly found in riverbeds and limestone outcrops.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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 (primarily SiO2)
sedimentary