sedimentary
Chert
Silicon Dioxide (Microcrystalline Quartz, $SiO_2$)
Hardness: 7 on the Mohs scale. Color: Varies widely from white, grey, and black to brown, red, or green. Luster: Vitreous to dull or waxy. Crystal structure: Microcrystalline or cryptocrystalline quartz (chalcedony/quartz aggregates). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.60 to 2.65.
- Hardness
- 7 on the Mohs scale
- Luster
- Vitreous to dull or waxy
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: 7 on the Mohs scale. Color: Varies widely from white, grey, and black to brown, red, or green. Luster: Vitreous to dull or waxy. Crystal structure: Microcrystalline or cryptocrystalline quartz (chalcedony/quartz aggregates). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.60 to 2.65.
Formation & geological history
Formed through chemical sedimentary processes, typically by the replacement of calcium carbonate in limestone by silica-rich solutions, or through the accumulation of microscopic siliceous skeletal remains (such as diatoms or radiolarians) in deep-marine environments over millions of years.
Uses & applications
Historically used extensively by early humans for making stone tools, arrowheads, and blades due to its sharp conchoidal fracture. Also used historically for striking fire with steel, and in modern aggregate or decorative landscaping.
Geological facts
Chert, flint, and jasper are all varieties of microcrystalline quartz. Flint is typically dark grey or black found in chalk, whereas chert is often lighter colored and found in limestone formations.
Field identification & locations
Can be identified in the field by its hard conchoidal fracture, sharp edges when broken, lack of reaction to hydrochloric acid, and hardness sufficient to scratch glass easily. Commonly found globally within 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