sedimentary
Chert (Flint variety)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: Dark grey to brown with tan cortex, Luster: Waxy to dull, Crystal structure: Microcrystalline/Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark grey to brown with tan cortex, Luster: Waxy to dull, Crystal structure: Microcrystalline/Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of siliceous remains of organisms (like diatoms or radiolarians) or chemical precipitation in sedimentary environments. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools and weapons (arrowheads); currently used for decorative stone, industrial grinding media, and as a component in certain ceramics.
Geological facts
Flint was one of the first materials harvested by early humans. It is famous for its ability to create sparks when struck against steel, a property used for centuries to start fires and fire muskets.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and sharp edges. It can scratch glass. Often has a lighter-colored weathered outer 'skin' or cortex.
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Brecciated Chert (Microcrystalline Silica)
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