sedimentary
Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Brown, tan, and gray; Luster: Waxy to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 6
- Color
- Brown, tan, and gray
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Brown, tan, and gray; Luster: Waxy to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed primarily in marine environments from the accumulation of siliceous remains of diatoms or radiolarians, or through chemical precipitation. This specific piece has been rounded and smoothed by water erosion in a river or beach environment.
Uses & applications
Historically used for making stone tools (arrowheads). Today used in landscaping, road construction, and occasionally for lapidary tumbling.
Geological facts
Chert is so durable that it often survives as smooth pebbles in riverbeds long after the surrounding rock has eroded. Some varieties with specific colors are known as Jasper or Flint.
Field identification & locations
Identify in the field by its smooth, waxy surface and its ability to scratch glass. It often shows curved, shell-like (conchoidal) fractures if chipped. Commonly found in gravel pits and along shorelines.
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