sedimentary
Chert River Pebble
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Dark grey to brownish-green; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Dark grey to brownish-green
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Dark grey to brownish-green; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich microfossils (like radiolarians or diatoms) on the ocean floor or through chemical precipitation in groundwater. This specimen has been rounded and smoothed by water transport in a river or coastal environment.
Uses & applications
Historically used for making stone tools (arrowheads/scrapers) due to its sharp edges; currently used as decorative gravel, in construction as aggregate, or as tumbled stones for collectors.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture creates edges sharper than a steel scalpel. It is chemically identical to flint but usually refers to lighter-colored or non-chalk-associated varieties.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, waxy texture. Look for the curved, shell-like (conchoidal) fractures on the surface. Commonly found in riverbeds and gravel pits.
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