sedimentary
Chert (Flint) River Pebble
Microcrystalline Quartz (SiO2)
AI-generated identification · may be incorrectHardness: 7 (Mohs scale), Color: Dark grey to black with tan exterior, Luster: Waxy to vitreous when polished, Structure: Cryptocrystalline, Fracture: Conchoidal
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark grey to black with tan exterior, Luster: Waxy to vitreous when polished, Structure: Cryptocrystalline, Fracture: Conchoidal
Formation & geological history
Formed as nodules or beds in limestone or chalk through the replacement of calcium carbonate by silica. Weathered and rounded by river or alluvial transport.
Uses & applications
Historically used for stone tools and fire-starting; currently used for river landscaping, decorative gravel, and lapidary tumbling.
Geological facts
Chert is so durable that it often survives long after the surrounding rock has eroded. Black chert is specifically known as flint and was prized by early humans for its predictable fracturing.
Field identification & locations
Identified by its smoothness, conchoidal fracture patterns (chips like glass), and its ability to scratch glass. Commonly found in riverbeds and glacial tills.
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