sedimentary
Chert Pebble
Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Brown/Opaque, Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Brown/Opaque, Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed via the accumulation of silica-rich organic remains or chemical precipitation in marine or freshwater environments. Often found as nodules or stream-rounded pebbles.
Uses & applications
Historically used for making stone tools; currently used in construction aggregate, road surfacing, and as decorative river stones.
Geological facts
Because it is harder than steel and breaks with sharp edges, chert was a primary material for prehistoric arrowheads and scrapers.
Field identification & locations
Identified in the field by its extreme hardness (scratches glass), smooth texture, and waxy luster. Commonly found in riverbeds and glacial deposits.
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