sedimentary
Chert (likely flint)
Microcrystalline quartz (SiO₂), chiefly chalcedony and quartz
AI-generated identification · may be incorrectTypically Mohs hardness 6.5–7, brown to gray, dense and opaque, with a dull to waxy luster and conchoidal fracture; no visible cleavage. The smooth, fine-grained texture and sharp fractured edge fit chert.
Identified More sedimentary →
Explore Chert (likely flint) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Typically Mohs hardness 6.5–7, brown to gray, dense and opaque, with a dull to waxy luster and conchoidal fracture; no visible cleavage. The smooth, fine-grained texture and sharp fractured edge fit chert.
Formation & geological history
Forms mainly by silica replacement of limestone or accumulation of microscopic siliceous remains, commonly during the Paleozoic–Cenozoic. Weathering can release durable nodules or cobbles from carbonate strata.
Uses & applications
Historically used for sharp tools, arrowheads, and fire-starting; today it is mainly a decorative, lapidary, aggregate, and teaching material.
Geological facts
Fresh fractures can produce exceptionally sharp edges because of conchoidal breakage. Brown coloration commonly reflects iron oxides or organic impurities.
Field identification & locations
Identify it by testing for glass-scratching hardness, very fine texture, lack of fizz in dilute acid, and curved fracture surfaces. Common in limestone regions worldwide, including river gravels and glacial deposits.
More like this
Other sedimentary specimens
Fossiliferous Sedimentary Rock
Sedimentary limestone with invertebrate fossil imprint
fossil
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite
sedimentary
Quartz pebble
Silicon dioxide (SiO2)
sedimentary
Sedimentary Sandstone
Arenite (Sedimentary Rock)
sedimentary
Generic Pebble / Rock Fragment
Lithic fragment / Weathered rock
sedimentary