Sedimentary
Chert / Flint
Cryptocrystalline quartz (SiO2)
Hardness: 6.5-7 (Mohs), Color: light gray, tan to brown, Luster: waxy to dull, Cleavage: none, exhibits conchoidal fracture.
- Hardness
- 6
- Luster
- waxy to dull, Cleavage: none, exhibits conchoidal fracture
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Physical properties
Hardness: 6.5-7 (Mohs), Color: light gray, tan to brown, Luster: waxy to dull, Cleavage: none, exhibits conchoidal fracture.
Formation & geological history
Formed from silica-rich fluids precipitating in limestone or chalk, or from the accumulation of siliceous marine microfossils (like radiolarians).
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its conchoidal fracture. Sometimes used as a sparkstriker with steel.
Geological facts
Because of its ability to hold a sharp edge, chert was one of the most important minerals for early human survival.
Field identification & locations
Identify by its waxy luster, hardness (scratches glass), and prominent curved, conchoidal fractures. Commonly found as nodules in sedimentary rock formations.
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