sedimentary
Chert (Flint)
Chert (Cryptocrystalline Quartz, SiO2)
Hardness: 7 (Mohs scale); Color: Gray, brown, or blackish; Luster: Waxy to dull; Crystal structure: Hexagonal (cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Gray, brown, or blackish
- 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 (Mohs scale); Color: Gray, brown, or blackish; Luster: Waxy to dull; Crystal structure: Hexagonal (cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed from the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or through the chemical precipitation of silica in marine or groundwater environments. It typically forms within limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads, knives) due to its sharp edges; used in modern times for road surfacing, grinding media, and occasionally as fire-starting 'flint' in survival gear.
Geological facts
Chert is so hard it can scratch glass and steel. High-quality dark gray or black chert is often specifically called 'flint' and was the most important material for early human toolmaking and early firearms (flintlocks).
Field identification & locations
Identify in the field by its very smooth, shell-like (conchoidal) fracture surfaces and its ability to spark when struck against steel. It is frequently found as nodules within limestone outcrops.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone (Quartz-rich)
Arenite (SiO2)
sedimentary
Sandstone (with man-made markings)
Arenite (composed primarily of Quartz, SiO2)
sedimentary