sedimentary
Chert Pebble
Microcrystalline quartz (SiO2)
Hardness: 7 (Mohs), Color: Brown/earthy tone, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Fracture: Conchoidal, Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs), Color: Brown/earthy tone, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Fracture: Conchoidal, Specific gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich organic remains or chemical precipitation in sedimentary basins. The rounded shape indicates significant water transport and erosion, likely from a riverbed or coastal environment.
Uses & applications
Historically used for stone tools/fire-starting; currently used as construction aggregate, decorative landscaping stone, and occasionally for lapidary tumbling.
Geological facts
Chert is so tough and chemically stable that it can survive long-distance transport in rivers that would grind other rocks to sand. It is often found as nodules within limestone or chalk beds.
Field identification & locations
Identify by its extreme hardness (scratches glass), smooth waxy feel, and conchoidal (shell-like) fracture if broken. This specimen is a typical 'river rock' found in gravel deposits globally.
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