sedimentary
Chert / Flint
Chert (Cryptocrystalline Quartz, SiO2)
Hardness: 7 (Mohs scale), Color: light gray to dark gray with waxy luster, Conchoidal fracture, Dense and opaque, Microcrystalline structure
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Physical properties
Hardness: 7 (Mohs scale), Color: light gray to dark gray with waxy luster, Conchoidal fracture, Dense and opaque, Microcrystalline structure
Formation & geological history
Formed by the precipitation of silica from seawater or groundwater, often occurring as nodules within limestone or chalk beds. Many deposits date from the Paleozoic or Mesozoic eras.
Uses & applications
Historically used for stone tools and starting fires; currently used as a raw material for ceramics, construction aggregate, and as a collectible specimen.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture allows it to be knapped into extremely sharp edges for arrowheads and scrapers.
Field identification & locations
Identify in the field by its hardness (it should scratch glass), waxy feel, and characteristic shell-like (conchoidal) breakage patterns. Common in sedimentary basins worldwide.
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