sedimentary
Chert (Chalcedony / Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs), Color: brownish-tan with white banding/weathering crust, Luster: waxy to dull, Structure: cryptocrystalline, Fracture: conchoidal (shell-like)
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Physical properties
Hardness: 7 (Mohs), Color: brownish-tan with white banding/weathering crust, Luster: waxy to dull, Structure: cryptocrystalline, Fracture: conchoidal (shell-like)
Formation & geological history
Formed via the accumulation of silica-rich fluids in sedimentary environments or by the replacement of carbonate materials. Often found in limestone or chalk beds.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges; modernly used as road aggregate, in jewelry (agate varieties), or for fire-starting.
Geological facts
Chert and flint are among the first materials used by humans to create technology. High-quality varieties that are translucent are often called chalcedony.
Field identification & locations
Identified by its extreme hardness (scratches glass), waxy luster on fresh surfaces, and smooth, curved fracture marks. Common in desert pavements and riverbeds.
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