sedimentary
Gray Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs), Color: Dark gray to light gray, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs), Color: Dark gray to light gray, 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 (like radiolarians or diatoms) or chemical precipitation in marine environments. This specimen is a rounded river pebble shaped by water erosion.
Uses & applications
Historically used for making stone tools and arrowheads; currently used in landscaping, as road aggregate, and for flint-knapping enthusiasts.
Geological facts
Chert is a variety of microcrystalline quartz that breaks with a conchoidal fracture, creating sharp edges that were vital to prehistoric human survival.
Field identification & locations
Look for a smooth, waxy surface and conchoidal (shell-like) fractures. It will scratch glass and won't react with acid, distinguishing it from limestone. Commonly found in riverbeds and limestone outcrops.
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