sedimentary
Chert (specifically Flint)
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness: 7.0 on Mohs scale; Color: typically dark grey, black, or brown; Luster: waxy to dull; Structure: microcrystalline (no visible grains); Cleavage: none, exhibits distinct conchoidal (shell-like) fracture; Specific Gravity: 2.65.
- Hardness
- 7
- Color
- typically dark grey, black, or brown
- Luster
- waxy to dull
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7.0 on Mohs scale; Color: typically dark grey, black, or brown; Luster: waxy to dull; Structure: microcrystalline (no visible grains); Cleavage: none, exhibits distinct conchoidal (shell-like) fracture; Specific Gravity: 2.65.
Formation & geological history
Formed in marine or freshwater environments via the replacement of carbonate minerals by silica-rich fluids. It often occurs as nodules or layers within limestone and chalk beds. Common in deposits from the Paleozoic and Mesozoic eras.
Uses & applications
Historically used for stone tools (arrowheads/knives) due to its sharp edges and as a fire-starting striking material. Modern uses include decorative gravel, road construction, and occasionally in gemstone tumbling.
Geological facts
Flint was a vital survival tool for prehistoric humans. When struck against steel (or iron pyrite), it creates hot sparks used for fire-making and was the mechanism for flintlock firearms.
Field identification & locations
Identify by its 'glassy' smooth texture when broken and razor-sharp edges. It is found globally, notably in the chalk cliffs of the UK and across North America. To identify, check for its ability to scratch glass and its curved, shell-like fracture pattern.
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