sedimentary
Chert (Flint)
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs), Color: Dark gray to black (flint) or brown/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: Dark gray to black (flint) or brown/tan, Luster: Waxy to vitreous, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in sedimentary environments. Often found as nodules within limestone or chalk beds.
Uses & applications
Historically used for stone tools and starting fires; currently used as a grinding media in ball mills, in road construction, and for aquarium decor.
Geological facts
Flint was the primary material for prehistoric survival, used to manufacture arrowheads and spear points due to its ability to hold a sharp edge when fractured conchoidally.
Field identification & locations
Identify by its very smooth, waxy surface and distinct shell-like (conchoidal) curves where it has chipped. Commonly found in riverbeds, chalk cliffs, and gravel pits.
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 (Quartz-rich)
Arenite (SiO2)
sedimentary
Sandstone (with man-made markings)
Arenite (composed primarily of Quartz, SiO2)
sedimentary