sedimentary
Chert (often called Flint or Jasper)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: can be white, grey, or tan; Luster: waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: none, breaks with conchoidal fracture.
- Hardness
- 6
- Color
- can be white, grey, or tan
- 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 on Mohs scale; Color: can be white, grey, or tan; Luster: waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: none, breaks with conchoidal fracture.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation from silica-rich fluids in limestone/dolomite layers.
Uses & applications
Historically used for stone tools (arrowheads/knives) due to sharp edges; currently used for road gravel, construction aggregate, and occasionally as a polishing stone.
Geological facts
Chert is so hard it can spark when struck against steel. It was one of the most vital materials for prehistoric humans globally for making survival tools and starting fires.
Field identification & locations
Identify by its waxy texture, hardness (it scratches glass), and the way it chips into sharp, curved 'shell-like' (conchoidal) flakes. Common in sedimentary basins worldwide.
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