sedimentary
Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, and grey; Luster: Waxy to vitreous when wet; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, and grey
- Luster
- Waxy to vitreous when wet
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, and grey; Luster: Waxy to vitreous when wet; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed primarily by the precipitation of silica in sedimentary environments or the replacement of limestone. These specific specimens are water-worn river pebbles smoothed via fluvial erosion over thousands of years.
Uses & applications
Used historically for stone tools due to sharp edges; currently used for landscaping, aggregate in construction, and as a tumbling material for rock hobbyists.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture allows it to be shaped into blades. Variations of chert include flint and jasper.
Field identification & locations
Identify by its hardness (cannot be scratched by a steel knife) and its smooth, rounded appearance in riverbeds. Common in gravel pits and along shorelines.
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