sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Black, grey, or brown often with a weathered white/tan cortex; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Luster
- Dull to waxy
Identified More sedimentary →
Explore Chert (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: Black, grey, or brown often with a weathered white/tan cortex; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed as nodules or layers in limestone or chalk through the accumulation of siliceous remains of marine organisms like diatoms and radiolarians. The silica precipitates and replaces calcite through diagenesis.
Uses & applications
Historically used for stone tools and weapons due to its sharp edges; modern uses include flintlocks for firearms, road surfacing, and as a raw material in ceramics.
Geological facts
Chert exhibits conchoidal fracture, allowing it to be chipped into extremely sharp blades. It was one of the most important minerals for prehistoric humans during the Stone Age.
Field identification & locations
Identify by its waxy luster on fresh surfaces and glass-like, sharp edges when broken. It will scratch glass but cannot be scratched by a steel knife. Common in limestone outcrops and riverbeds.
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