sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Gray/Blue-gray, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Gray/Blue-gray, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or chemical precipitation from silica-rich fluids in limestone/chalk beds.
Uses & applications
Historically used for stone tools and weapons (arrowheads); currently used in road construction, gemstone tumbling, and as a component in certain ceramics.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture produces extremely sharp edges, foundational for the development of prehistoric technology.
Field identification & locations
Identify by its waxy luster, extreme hardness (scratches glass), and distinctive curved (conchoidal) shell-like break patterns. Commonly found in nodular forms within limestone.
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