sedimentary
Chert (Flint)
Microcrystalline silica (SiO2)
Hardness 7 (Mohs), tan to gray color, waxy to dull luster, cryptocrystalline structure, conchoidal fracture, specific gravity 2.6
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), tan to gray color, waxy to dull luster, cryptocrystalline structure, conchoidal fracture, specific gravity 2.6
Formation & geological history
Formed as nodules or layers in limestone or chalk through the precipitation of silica from groundwater or biological sources (diatoms/sponges).
Uses & applications
Historically used for stone tools and fire-starting; currently used as construction aggregate or decorative landscape stone.
Geological facts
Chert breaks with a conchoidal (shell-like) fracture, producing very sharp edges which is why it was the primary material for arrowheads and scrapers in prehistoric times.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and smooth, curved break patterns. Commonly found in stream beds or eroding out of limestone cliffs.
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
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary