sedimentary
Chert (Flint)
Cryptocrystalline Quartz (SiO2)
Hardness (7 on Mohs scale), color (tan to gray-blue), waxy to dull luster, cryptocrystalline structure, conchoidal fracture, specific gravity 2.6-2.7
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Physical properties
Hardness (7 on Mohs scale), color (tan to gray-blue), waxy to dull luster, cryptocrystalline structure, conchoidal fracture, specific gravity 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments, typically where silica replaces carbonate minerals in limestone or chalk beds.
Uses & applications
Historically used for stone tools and starting fires (striking steel). Today used as road surfacing material and in jewelry (as jasper or flint).
Geological facts
Flint was one of the first materials traded over long distances by prehistoric humans due to its ability to hold a sharp edge. It is virtually immune to chemical weathering.
Field identification & locations
Identify by its 'shell-like' conchoidal fracture pattern and hardness (it will scratch glass). Often found as nodules within limestone or as river-worn pebbles. Look for a smooth, waxy surface on broken faces.
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