sedimentary
Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Brownish-tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None, exhibits conchoidal fracture; Specific gravity: approx 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Brownish-tan
- Luster
- Waxy to dull
Identified More sedimentary →
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Physical properties
Hardness: 7 (Mohs scale); Color: Brownish-tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None, exhibits conchoidal fracture; Specific gravity: approx 2.65
Formation & geological history
Formed via the accumulation of silica-rich organic remains or chemical precipitation in sedimentary basins. The rounded shape indicates it is a stream-worn or river-tumbled pebble originating from the erosion of larger nodules.
Uses & applications
Historically used for stone tools (flintknapping); currently used as decorative gravel, in landscaping, or as a low-cost specimen for geology hobbyists.
Geological facts
Chert has been used by humans for millions of years to make arrowheads and tools because it breaks with sharp edges. It is often found as nodules in limestone or chalk beds.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by steel), waxy appearance, and smooth, rounded surface indicating water transport. Commonly found in riverbeds, gravel pits, and glacial till.
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