sedimentary
Chert (and Jasper blend)
Chert (Microcrystalline Quartz, SiO2)
Hardness: 6.5-7 (Mohs scale), Color: variegated grey, beige, and tan with subtle banding, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.6-2.7
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: variegated grey, beige, and tan with subtle banding, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within sedimentary rock layers, predominantly during various geological eras from the Precambrian onwards.
Uses & applications
Historically used for stone tools (arrowheads/scrapers) due to sharp edges; currently used as decorative gravel, in lapidary work for cabochons, and as a collector's specimen.
Geological facts
Chert is so durable that it was one of the primary materials used by prehistoric humans to create fire through striking against steel or other hard rocks. This specific specimen appears water-worn or tumbled, smoothing its naturally jagged edges.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a steel knife) and its characteristic shell-like (conchoidal) fracture pattern. Commonly found in limestone or chalk beds, riverbanks, and beaches.
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