sedimentary
Flint (or Chert)
Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, black, or brown; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Gray, black, or brown
- Luster
- Waxy to vitreous
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 on Mohs scale; Color: Gray, black, or brown; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed as nodules in sedimentary rocks like chalk or marine limestone. It originates from the accumulation of silica-rich organic remains (like sponge spicules or radiolaria) that dissolve and reprecipitate during diagenesis.
Uses & applications
History's most important stone for tool-making (arrowheads, knives). Used today in ceramics, as an abrasive, in road construction, and occasionally for 'flintlock' ignition mechanisms. Collectors value worked artifacts and unique nodules.
Geological facts
Flint was the first 'commodity' traded by humans. Because it breaks with incredibly sharp edges, surgical scalpels made of flint are sharper than high-quality steel blades on a microscopic level.
Field identification & locations
Identify by its 'waxy' texture and conchoidal (shell-like) fracture patterns. It often has a white outer 'cortex'. Found globally, notably on beaches in the UK, France, and Northern Europe, and in limestone regions of North America.
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