sedimentary
Chert (Nodule)
Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Brownish-tan to earthy beige, Luster: Dull/Waxy, Crystal Structure: Microcrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Brownish-tan to earthy beige, Luster: Dull/Waxy, Crystal Structure: Microcrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich fluids in limestone or chalk beds, often replacing organic material or filling cavities. Many specimens are Mesozoic or Paleozoic in age.
Uses & applications
Historically used for stone tools (flintknapping); currently used in road construction, landscaping, and as a collector's specimen.
Geological facts
Chert is so hard it can scratch steel. It was one of the most important minerals for early humans because of its ability to break into extremely sharp edges for knives and arrowheads.
Field identification & locations
Identified in the field by its hardness, smooth waxy texture when broken, and frequent occurrence as nodules in limestone. If struck with steel, it may produce sparks.
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