sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs), Color: Tan to grey, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs), Color: Tan to grey, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65
Formation & geological history
Formed primarily by the biochemical or chemical precipitation of silica in marine environments, often replacing calcium carbonate in limestone or forming as nodules in deep-sea sediments.
Uses & applications
Historically used for stone tools and arrowheads; currently used as construction aggregate, in road surfacing, and as a raw material for silicon production.
Geological facts
Chert is essentially the same as flint, though 'flint' usually refers to chert found in chalk or marl formations. It can preserve microfossils in extreme detail.
Field identification & locations
Identify by its extreme hardness (scratches glass), waxy appearance, and characteristic curved (conchoidal) fractures when broken. Commonly found in coastal areas and riverbeds.
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