sedimentary
Chert
Sedimentary Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: typically earthy browns, tans, or grays; Luster: waxy to dull; Crystal structure: cryptocrystalline (microscopic); Cleavage: none (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- typically earthy browns, tans, or grays
- 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 on Mohs scale; Color: typically earthy browns, tans, or grays; Luster: waxy to dull; Crystal structure: cryptocrystalline (microscopic); Cleavage: none (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. Commonly found in Paleozoic and Mesozoic strata.
Uses & applications
Historically used for making stone tools (arrowheads and scrapers) due to its sharp edges; used today as a construction aggregate and occasionally as a flint for fire-starting.
Geological facts
Chert is so hard it can scratch steel and glass. In its darker, more lustrous form, it is known as flint. It has been used by humans for over 2 million years.
Field identification & locations
Identify by its 'conchoidal' (shell-like) fracture pattern and its inability to be scratched by a steel knife. Commonly found as nodules or layers within limestone outcrops.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary