sedimentary
Chert / River Pebble
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: tan-brown with iron staining, Luster: dull to waxy, Crystal Structure: Microcrystalline quartz, Cleavage: None (conchoidal fracture)
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Physical properties
Hardness: 7 (Mohs scale), Color: tan-brown with iron staining, Luster: dull to waxy, Crystal Structure: Microcrystalline quartz, Cleavage: None (conchoidal fracture)
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolarians) or chemical precipitation in marine or freshwater environments. Smooth shape indicates mechanical weathering in a river or stream bed.
Uses & applications
Used historically for stone tools (arrowheads), as construction aggregate, or in flint-knapping. Tumbled specimens are used for decoration and landscaping.
Geological facts
Chert is extremely durable and chemically stable, allowing it to survive thousands of years of erosion. It was one of the most important minerals for early human technological development.
Field identification & locations
Identify by its 'glassy' smooth texture when broken and its ability to scratch glass. Found globally in riverbeds, gravel pits, and sedimentary rock formations like limestone.
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