sedimentary
Yellow Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: yellowish-tan; Luster: waxy to dull; Structure: Cryptocrystalline; Cleavage: No true cleavage (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- yellowish-tan
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: yellowish-tan; Luster: waxy to dull; Structure: Cryptocrystalline; Cleavage: No true cleavage (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich microfossils like diatoms or radiolarians, or via chemical precipitation from circulating fluids. It is often found as nodules or pebbles reshaped by river transport over millions of years.
Uses & applications
Historically used for stone tools (arrowheads). In modern times, used as decorative aggregate, landscaping rock, and occasionally tumble-polished by hobbyists.
Geological facts
Chert was one of the most vital materials for early humans because its conchoidal fracture produces extremely sharp edges. Yellow variants often get their color from iron oxide (limonite) impurities.
Field identification & locations
Look for a smooth, waxy texture and 'shell-like' curved fractures on broken edges. Commonly found in riverbeds, gravel pits, and coastal areas throughout North America and Europe.
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