sedimentary
Chert (River Pebble)
Microcrystalline silica (SiO2)
Hardness: 6.5-7 Mohs; Color: greyish-green to tan; Luster: waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- greyish-green to tan
- Luster
- waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: greyish-green to tan; Luster: waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or freshwater environments. This specimen has been rounded and smoothed by water transport (river action).
Uses & applications
Historically used for stone tools (arrowheads); currently used as road aggregate, architectural stone, or decorative landscaping pebbles.
Geological facts
Chert is so hard it can scratch steel and was once highly valued by indigenous peoples for its ability to produce a sharp edge when knapped.
Field identification & locations
Identify by its hardness (cannot be scratched by a knife), smooth texture, and curved 'conchoidal' fractures. Often found in riverbeds or coastal deposits.
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