sedimentary
Brown Chert
Cryptocrystalline Silica (SiO2)
Hardness: 7 (Mohs), Color: Brown/Grey, Luster: Waxy to Dull, Crystal structure: Microcrystalline, Cleavage: None (Conchoidal fracture), Specific Gravity: 2.65
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 (Mohs), Color: Brown/Grey, Luster: Waxy to Dull, Crystal structure: Microcrystalline, Cleavage: None (Conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed in marine environments through the precipitation of silica-rich fluids or the accumulation of siliceous skeletal remains (like diatoms or radiolarians). It forms within sedimentary rock layers like limestone or chalk.
Uses & applications
Historically used for stone tools and arrowheads. Currently used as an aggregate in construction, road surfacing, and as a polishing media. Fine specimens are used for folk art and flint knapping.
Geological facts
Chert has been used by humans for over 2 million years because it breaks with a razor-sharp conchoidal fracture. Some varieties contain well-preserved microfossils and can vary greatly in color based on mineral impurities.
Field identification & locations
Identify by its waxy luster, extreme hardness (it scratches glass), and curved glass-like fractures. It is commonly found as nodules or layers within limestone beds or as smoothed river stones.
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