sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan, beige, gray, or white, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, beige, gray, or white, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed via the accumulation of silica-rich organic remains (such as diatoms or radiolaria) or through chemical precipitation from silica-rich fluids within limestone or chalk beds. Commonly found in Paleozoic and Mesozoic sedimentary strata.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges; modernly used as a decorative stone in landscaping, jewelry (as 'jasper' when colored), and in road construction aggregate.
Geological facts
Chert and flint were among the first materials used by prehistoric humans to start fires and manufacture survival tools. It is so hard that it can scratch steel and glass.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. Commonly found as nodules or layers within limestone formations globally.
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