sedimentary
Chert
Microcrystalline quartz (SiO2)
Hardness of 7 on the Mohs scale; colors vary widely from white, grey, brown to black; vitreous to waxy luster; cryptocrystalline structure; conchoidal fracture with no true cleavage; specific gravity around 2.60 to 2.65.
Identified More sedimentary →
Explore Chert in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness of 7 on the Mohs scale; colors vary widely from white, grey, brown to black; vitreous to waxy luster; cryptocrystalline structure; conchoidal fracture with no true cleavage; specific gravity around 2.60 to 2.65.
Formation & geological history
Formed through the chemical precipitation of silica from aqueous solutions, often derived from the skeletal remains of microscopic marine organisms like diatoms or radiolarians, accumulating on ocean floors over millions of years.
Uses & applications
Historically used by early humans for making stone tools such as arrowheads, spear points, and blades due to its sharp conchoidal fracture. Also used in abrasives and occasionally as a decorative or ornamental stone.
Geological facts
Chert is a very durable and resilient rock that resists weathering better than surrounding limestone formations, often standing out as nodules or layers in eroding cliffs.
Field identification & locations
Identified easily by its extreme hardness (scratches glass), waxy to dull luster, and distinct smooth conchoidal fracture resembling broken glass. Found worldwide in sedimentary sequences, particularly limestone and chalk deposits.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Quartz pebble
Silicon dioxide (SiO2)
sedimentary
Fossiliferous Concretion
Septarian Concretion containing Brachiopods/Crinoids
fossil
Generic Pebble / Rock Fragment
Lithic fragment / Weathered rock
sedimentary
Sedimentary Sandstone
Arenite (Sedimentary Rock)
sedimentary
Banded Siltstone / Mudstone Pebble
Siltstone / Argillite
sedimentary