sedimentary
Chert (Jasper-rich River Cobble)
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Brownish-red to orange due to iron oxide (limonite/hematite). Luster: Dull to waxy. Structure: Microcrystalline with no visible grains. Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Brownish-red to orange due to iron oxide (limonite/hematite)
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Brownish-red to orange due to iron oxide (limonite/hematite). Luster: Dull to waxy. Structure: Microcrystalline with no visible grains. Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the chemical precipitation of silica or the replacement of limestone by silica-rich fluids. This specific specimen is a water-worn river cobble, rounded by mechanical weathering in a high-energy fluvial environment.
Uses & applications
Abrasives, decorative landscaping, historical tool-making (flintknapping), and basic jewelry cabochons.
Geological facts
Chert is so durable that it can survive millions of years of river transport. It was the primary material used by prehistoric humans for creating sharp-edged tools like arrowheads and scrapers.
Field identification & locations
Identify by its hardness (it will scratch glass), smooth waxy texture when wet, and curved 'conchoidal' fractures on broken edges. Common in riverbeds and limestone regions.
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