sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Gray, tan, or black with white outer cortex, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Identified More sedimentary →
Explore Chert (Flint) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 (Mohs scale), Color: Gray, tan, or black with white outer cortex, Luster: Waxy to dull, Crystal 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 by chemical precipitation from groundwater within limestone or chalk beds. Often Cretaceous in age.
Uses & applications
Historically used for stone tools and fire-starting. Currently used in road construction, as architectural stone, and for decorative lapidary work.
Geological facts
Flint is a variety of chert that was the most important raw material for early humans to create sharp-edged tools like arrowheads and knives due to its predictable conchoidal fracturing.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and curved, glass-like fracture surfaces. Often found as nodules within limestone or as rounded river cobbles.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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 (primarily SiO2)
sedimentary