sedimentary
Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: tan, grey, or cream; Luster: waxy to dull; Breakage: conchoidal fracture (curved surfaces); Texture: very fine-grained.
- Hardness
- 6
- Color
- tan, grey, or cream
- Luster
- waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: tan, grey, or cream; Luster: waxy to dull; Breakage: conchoidal fracture (curved surfaces); Texture: very fine-grained.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation in marine or groundwater environments. This specimen appears water-worn, suggesting transport in a river or stream.
Uses & applications
Historically used for making stone tools (arrowheads/scrapers) due to its sharp edges; industrially used in road construction as gravel or as a component in glass making.
Geological facts
Chert is extremely durable and chemically stable, which is why it often survives as rounded pebbles in streambeds long after other rocks have eroded away. Varieties include flint and jasper.
Field identification & locations
Identify by its 'waxy' appearance and the way it breaks in curved, shell-like patterns. Common in sedimentary basins worldwide. Often found in gravel bars.
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