sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
AI-generated identification · may be incorrectHardness: 7 (Mohs scale), Color: dull gray to brown, Luster: waxy to dull, Structure: microcrystalline, Cleavage: none (conchoidal fracture)
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Physical properties
Hardness: 7 (Mohs scale), Color: dull gray to brown, Luster: waxy to dull, Structure: microcrystalline, Cleavage: none (conchoidal fracture)
Formation & geological history
Formed as nodules in limestone or chalk through the replacement of calcium carbonate by silica-rich fluids. Often dates from the Cretaceous period.
Uses & applications
Historically used for stone tools and starting fires (striking steel). Modernly used in construction aggregate and road surfacing.
Geological facts
Chert was one of the most important materials for early human technology. When broken, it creates edges sharper than a steel scalpel.
Field identification & locations
Identify by its extremely smooth, shell-like fracture surfaces and ability to scratch glass. Found globally in sedimentary basins.
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