sedimentary
Flint or Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Dark grey to black with white/tan weathering, Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture)
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark grey to black with white/tan weathering, Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture)
Formation & geological history
Formed as nodules in sedimentary rocks like chalk or marine limestones through a process where silica-rich fluids replace carbonate material.
Uses & applications
Historically used for stone tools and starting fires; currently used as a grinding medium in ball mills or as landscaping and decorative stone.
Geological facts
Flint was the most essential technology for early humans, used for making arrowheads and axes due to its ability to break into razor-sharp edges.
Field identification & locations
Identified by its extremely smooth, glass-like fracture surfaces and high hardness (it can scratch glass). Commonly found in chalk deposits and riverbeds.
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