sedimentary
Chert
Microcrystalline Quartz (SiO2)
AI-generated identification · may be incorrectHardness: 7 (Mohs scale), Color: tan/brown/yellow, Luster: waxy to dull, Structure: microcrystalline (no visible grains), Cleavage: none (conchoidal fracture)
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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.
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