sedimentary
Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: Tan, beige, gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 Mohs scale
- Color
- Tan, beige, gray
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Tan, beige, gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed via the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. This specimen shows significant rounding from fluvial (river) or beach wear.
Uses & applications
Historically used for stone tools (flint knapping); currently used as drainage gravel, road base, and occasionally as decorative landscaping stone.
Geological facts
Chert can contain microfossils. It is extremely chemically stable and hard, which allows it to survive long-distance transport in rivers, becoming the smooth pebbles often found on beaches and in stream beds.
Field identification & locations
Identify by its smooth, waxy feel, conchoidal (shell-like) fracture patterns where broken, and high hardness (it will scratch glass). Found globally in sedimentary basins.
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