sedimentary
Chert (often called Flint or River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed by the precipitation of silica from groundwater or within biological remains in marine sedimentary environments. This specimen appears water-worn, likely from a stream or river bed.
Uses & applications
Historically used for stone tools and starting fires (striking steel). Modern uses include road aggregates, decorative landscaping stones, and tumbling for hobbyist collections.
Geological facts
Chert is so durable that it often survives long after the surrounding limestone or chalk has eroded away. Prehistoric humans prized it for its ability to fracture into razor-sharp edges.
Field identification & locations
Identify in the field by its smooth, waxy surface and its ability to scratch glass. This specific piece shows significant water erosion, creating a 'pitted' or 'pocketed' appearance. Common globally in sedimentary basins.
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