sedimentary
Chert (Iron-stained)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: tan to reddish-brown, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture)
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: tan to reddish-brown, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture)
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. This specimen shows iron oxide staining.
Uses & applications
Historically used for stone tools/flintknapping; currently used in construction aggregate and for lapidary tumbling.
Geological facts
Chert is so tough and chemically stable that it often survives as rounded pebbles in riverbeds long after surrounding rocks have eroded away.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture pattern. Found in riverbeds and limestone outcrops.
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