sedimentary
Chert (Flint)
Microcrystalline Silicon Dioxide (SiO2)
Hardness: 7 Mohs; Color: Brownish-black/Greyish; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 Mohs
- Color
- Brownish-black/Greyish
- Luster
- Waxy to dull
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 Mohs; Color: Brownish-black/Greyish; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed primarily from the accumulation of silica-rich organic remains (like radiolaria or diatoms) in marine environments, compacting over millions of years into dense rock nodules.
Uses & applications
Historically used for stone tools (arrowheads/knives) due to sharp edges; used in modern times for road surfacing, as grinding media, and for sparking fire.
Geological facts
Chert and flint were among the first materials used by early humans for tool-making. Because it breaks with a conchoidal fracture (like glass), it creates extremely sharp edges.
Field identification & locations
Identified by its waxy luster, extreme hardness (scratches glass), and shell-like (conchoidal) fracture pattern. Found in limestone or chalk deposits.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Fossiliferous Concretion
Septarian Concretion containing Brachiopods/Crinoids
fossil
Shale
Shale (clastic sedimentary rock)
sedimentary
Brown Sandstone (River Rock)
Arenite
sedimentary
Mudstone
Argillite / Siliciclastic sedimentary rock
sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
sedimentary