sedimentary
Chert / Flint
Silicon dioxide (Microcrystalline Quartz, $SiO_2$)
Hardness of 7 on the Mohs scale, typically white, gray, or brown in color, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture with very sharp edges, specific gravity around 2.60.
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Physical properties
Hardness of 7 on the Mohs scale, typically white, gray, or brown in color, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture with very sharp edges, specific gravity around 2.60.
Formation & geological history
Formed through the chemical precipitation of silica from aqueous solutions or the replacement of calcium carbonate in limestone by silica during diagenesis, occurring over millions of years.
Uses & applications
Historically used for making stone tools, arrowheads, and fire-starting (striking against steel); modern uses include abrasives and road aggregates.
Geological facts
Chert and flint are essentially the same material; the term 'flint' is typically reserved for darker varieties found in chalk formations. It was one of the most critical materials for prehistoric human survival.
Field identification & locations
Easily identified by its conchoidal fracture (smooth, curved shell-like breaks), hardness capable of scratching glass, and waxy luster. Commonly found nodules within chalk or limestone deposits worldwide.
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