sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan/brown/yellow, Luster: waxy to dull, Structure: microcrystalline (no visible grains), Cleavage: none (conchoidal fracture)
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 (Mohs scale), Color: tan/brown/yellow, Luster: waxy to dull, Structure: microcrystalline (no visible grains), Cleavage: none (conchoidal fracture)
Formation & geological history
Formed by the precipitation of silica in sedimentary environments, often replacing calcium carbonate in limestone or through the accumulation of siliceous plankton remains. Most common in ancient marine deposits.
Uses & applications
Historically used for making stone tools (arrowheads). Currently used in road construction, as landscaping gravel, and as a durable abrasive in tumbling.
Geological facts
Chert was one of the most important minerals for early humans because of its conchoidal fracture, which produced razor-sharp edges. Flint is a dark variety of chert.
Field identification & locations
Identify by its extreme hardness (will scratch glass and common steel) and its concave, shell-like fracture pattern. Commonly found in riverbeds and limestone outcrops.
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