sedimentary
Chert (with Quartz)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Dark grey to black with white quartz, Luster: Waxy to vitreous, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark grey to black with white quartz, Luster: Waxy to vitreous, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal
Formation & geological history
Formed as chemical precipitates from silica-rich fluids in sedimentary environments or as nodules within limestone/chalk beds through the replacement of calcium carbonate.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to conchoidal fracture which creates sharp edges. Today used in construction aggregate and as decorative pebbles.
Geological facts
Chert is so hard it can produce sparks when struck against steel, which made it essential for flintlock firearms in historical warfare.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds or within limestone outcrops.
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