sedimentary
Chert
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale, Color: Varies from white, grey, brown to black, Luster: Waxy to vitreous, Crystal structure: Microcrystalline quartz (chalcedony), Cleavage: None (conchoidal fracture), Specific gravity: 2.6 - 2.65
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Physical properties
Hardness: 7 on Mohs scale, Color: Varies from white, grey, brown to black, Luster: Waxy to vitreous, Crystal structure: Microcrystalline quartz (chalcedony), Cleavage: None (conchoidal fracture), Specific gravity: 2.6 - 2.65
Formation & geological history
Formed by the precipitation of silica from water or replacement of limestone/chalk by silica-rich solutions during diagenesis.
Uses & applications
Historically used for making stone tools, arrowheads, and spark generation; currently used in abrasives and occasionally decorative items.
Geological facts
Chert often forms nodules in limestone formations and was a primary material for prehistoric stone tool manufacturing due to its sharp conchoidal fracture.
Field identification & locations
Easily identified by its hard conchoidal fracture, waxy luster, and lack of reaction to acid. Commonly found in limestone and chalk deposits worldwide.
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