sedimentary
Chert (Flint)
Chert (SiO2)
Hardness: 7 (Mohs scale), Color: Dark brown to black, Luster: Waxy or dull, Crystal structure: Microcrystalline quartz, Cleavage: None (conchoidal fracture), Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark brown to black, Luster: Waxy or dull, Crystal structure: Microcrystalline quartz, Cleavage: None (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed in marine environments through the precipitation of silica-rich fluids or the accumulation of siliceous skeletal remains (radiolarians/diatoms) within limestone or shale beds.
Uses & applications
Historically used for making stone tools (arrowheads). Today used in road construction, as an abrasive, and by survivalists for fire-starting.
Geological facts
Chert has been used by humans for over 2 million years. It is chemically stable and extremely resistant to weathering. High-quality varieties like Flint were among the first internationally traded commodities in human history.
Field identification & locations
Identify by its smooth, waxy feel and distinct shell-like (conchoidal) fracture when broken. This specific specimen is a water-worn river pebble. Common in sedimentary basins worldwide.
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