sedimentary
Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs, Color: Dark brown to black with tan inclusions, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, specific gravity: 2.65
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Physical properties
Hardness: 7 Mohs, Color: Dark brown to black with tan inclusions, 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 marine or freshwater environments. This specific specimen has been rounded by fluvial (river) erosion over thousands of years.
Uses & applications
Commonly used in prehistoric times for stone tools (lithics) due to its sharp edges; currently used for landscaping, road aggregate, and as a collector's item for rock tumbling.
Geological facts
Chert is so hard that it can strike sparks from steel, which led to its use in flintlock firearms. Some specimens contain microfossils visible only under high magnification.
Field identification & locations
Identified by its high hardness (doesn't scratch with steel), waxy texture, and smooth, rounded shape. Found in riverbeds, beaches, and glacial deposits worldwide.
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