sedimentary
Chert (Flint)
Chert (SiO2)
Hardness: 7 (Mohs scale), Color: tan/beige/gray, Luster: waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: tan/beige/gray, Luster: waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in marine environments. Typically found as nodules in limestone or chalk beds.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges; used today as road gravel, in ceramics, and occasionally as an abrasive.
Geological facts
Chert is so hard it can scratch steel. When struck against steel, it produce sparks, making it a primary material for flintlock firearms and fire-starting throughout history.
Field identification & locations
Identify in the field by its very smooth, waxy surface and shell-like (conchoidal) fractures. It is commonly found in gravel pits, riverbeds, or embedded in limestone outcrops.
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