sedimentary
Chert (Flint Nodules)
Microcrystalline silica (SiO2)
Hardness: 6.5-7 Mohs; Color: Brown, tan, or grey interior with white chalky cortex; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6
- Hardness
- 6
- Color
- Brown, tan, or grey interior with white chalky cortex
- Luster
- Waxy to dull
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.5-7 Mohs; Color: Brown, tan, or grey interior with white chalky cortex; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6
Formation & geological history
Formed in marine environments through the replacement of calcium carbonate by silica-rich fluids. Often found as nodules within limestone or chalk beds from the Cretaceous period.
Uses & applications
Historically used for stone tools (knapping) and fire-starting. Currently used in road construction, landscape gravel, and occasionally for lapidary work.
Geological facts
Flint was the primary material for human tools for over two million years. It creates sparks when struck against steel due to its hardness and friction, leading to its name "flint" from the Old English for "hard rock."
Field identification & locations
Identify by its extremely sharp edges when broken and its characteristic conchoidal (shell-like) fracture pattern. Commonly found in river beds or erosion sites near limestone deposits.
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
Arenite
sedimentary
Sandstone (Quartz-rich)
Arenite (SiO2)
sedimentary