sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: Dark grey to black, Luster: Waxy to dull, Crystal structure: Microcrystalline/cryptocrystalline, Cleavage: None (shows conchoidal fracture), Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark grey to black, Luster: Waxy to dull, Crystal structure: Microcrystalline/cryptocrystalline, Cleavage: None (shows conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed through the accumulation and replacement of siliceous organisms (like diatoms or radiolarians) or chemical precipitation in marine environments. Often found as nodules within limestone or chalk beds.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) and starting fires (flint and steel). Currently used as a road aggregate, in jewelry (as gemstones), and for decorative carvings.
Geological facts
Chert was one of the most important minerals for early humans due to its ability to break into sharp edges. It is extremely chemically stable and resistant to weathering.
Field identification & locations
Look for a smooth waxy texture and shell-like (conchoidal) fractures. It will scratch glass easily. Commonly found in limestone outcrops, river beds, and coastal areas.
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