sedimentary
Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, or grey; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 6
- Color
- Brown, tan, or grey
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, or grey; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation within sedimentary layers. This specific specimen is a water-worn river pebble, shaped by fluvial erosion over thousands of years.
Uses & applications
Historically used for stone tools (arrowheads). Modern uses include construction aggregate, road base, and occasionally decorative landscaping.
Geological facts
Chert is extremely durable and chemically stable. Because it breaks with a sharp edge, it was one of the most important minerals for early human survival for making tools and starting fires (flint is a variety of chert).
Field identification & locations
Identify by its hardness (it will scratch glass) and its smooth, rounded surface from water tumbling. Often found in riverbeds, glacial till, and coastal areas.
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