sedimentary
Chert (Yellow Jasper/River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Opaque yellowish-brown, Luster: Dull to waxy, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Opaque yellowish-brown, Luster: Dull to waxy, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed from the precipitation of silica in sedimentary environments, often originally from the skeletons of marine organisms like diatoms or radiolaria. This specific piece has been water-worn into a smooth pebble shape.
Uses & applications
Used historically for stone tools due to its sharp edges when broken. Today, utilized for decorative landscaping, lapidary tumbling, and jewelry-making when high quality.
Geological facts
Chert and its varieties like Jasper are among the most durable rocks, often surviving river transport for hundreds of miles. Early humans prized these stones for making arrowheads and scrapers.
Field identification & locations
Identified by its high hardness (will scratch glass), smooth texture, and lack of visible grains. Common in riverbeds, glacial deposits, and sedimentary basins worldwide.
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