sedimentary
Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs). Color: Variegated brown, tan, and dark grey. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6.
- Hardness
- 6
- Color
- Variegated brown, tan, and dark grey
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 (Mohs). Color: Variegated brown, tan, and dark grey. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6.
Formation & geological history
Formed from the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. This specific specimen has been smoothed and rounded by water erosion (fluvial transport).
Uses & applications
Primarily used as decorative landscaping stone, aggregate in construction, or for lapidary tumbling. Historically used for stone tools due to its sharp conchoidal fracture.
Geological facts
Chert is so durable that it often survives long after the surrounding rock has eroded away. It is essentially a non-banded form of chalcedony.
Field identification & locations
Identify by its hardness (it will scratch glass), smooth water-worn surface, and lack of visible grains. Common in riverbeds, gravel pits, and glacial till worldwide.
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