sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: Dark brown to grey/black, Luster: Waxy to vitreous, Crystal Structure: Cryptocrystalline (microscopic quartz), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark brown to grey/black, Luster: Waxy to vitreous, Crystal Structure: Cryptocrystalline (microscopic quartz), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.65
Formation & geological history
Formed from the precipitation of silica-rich fluids or the accumulation of siliceous skeletal remains (like diatoms or radiolaria) in marine environments. Often found as nodules within limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads, knives) due to sharp edges; currently used for road surfacing, as an abrasive, and in fire-starting kits.
Geological facts
Flint was one of the most important minerals for early human survival because of its ability to produce sharp edges and sparks when struck against steel or pyrite.
Field identification & locations
Identify by its 'shell-like' conchoidal fracture which leaves razor-sharp edges and its ability to scratch glass. Commonly found in river beds or sedimentary outcrops.
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