sedimentary
Flint / Chert
Silicon dioxide (SiO2)
Hardness: 7 (Mohs), Color: Grey, black, or tan, Luster: Waxy to vitreous, Structure: Cryptocrystalline, 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: Grey, black, or tan, Luster: Waxy to vitreous, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed in sedimentary rocks, typically as nodules in limestone or chalk through the replacement of calcium carbonate by silica. Often Cretaceous or Jurassic in age.
Uses & applications
Historically used for tools (knapping), fire-starting (sparking with steel), and construction in flint-walled buildings. Used in high-grade ceramics and chemical industry.
Geological facts
Flint is technically a variety of chert. It was the most important material for early human technology, used to make arrowheads and skinscrapers.
Field identification & locations
Identify by its characteristic conchoidal fracture (curved, shell-like breaks) and sharp edges. Common in coastal areas with chalk cliffs or river beds.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary