sedimentary
Chert / Flint
Microcrystalline Quartz (SiO2)
Hardness of 7 on the Mohs scale; colors range from dark gray, green, brown to black; waxy to vitreous luster; microcrystalline or cryptocrystalline crystal structure; conchoidal fracture with no true cleavage; specific gravity around 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale; colors range from dark gray, green, brown to black; waxy to vitreous luster; microcrystalline or cryptocrystalline crystal structure; conchoidal fracture with no true cleavage; specific gravity around 2.60 to 2.65.
Formation & geological history
Formed by the chemical precipitation of silica from aqueous solutions, often replacing carbonate rocks like limestone in marine environments over millions of years.
Uses & applications
Historically used by early humans for stone tools, arrowheads, and fire-starting (flint and steel); occasionally used in decorative landscaping, abrasive grinding, or knapping displays.
Geological facts
Chert is extremely durable and weathering-resistant, which is why ancient stone tools made of chert often survive intact in the archaeological record for tens of thousands of years.
Field identification & locations
Can be identified in the field by its distinct conchoidal fracture (smooth, curved breakage surfaces) and high hardness that readily scratches glass.
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