sedimentary
Chert (Jasper variety)
Chert (Silicon Dioxide, SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown and tan; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline (Trigonal); Cleavage: None (Conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Reddish-brown and tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown and tan; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline (Trigonal); 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. This specimen shows water-worn rounding, likely from a fluvial or coastal environment.
Uses & applications
Historically used for stone tools (arrowheads) due to conchoidal fracture. Currently used in jewelry as semi-precious gemstones (Jasper), landscaping, and as a collector's item.
Geological facts
Chert is so durable it often survives millions of years of erosion that destroys other rocks. It was one of the first materials used by early humans for fire-starting and weaponry.
Field identification & locations
Identify in the field by its hardness (scratches glass), smooth waxy texture, and shell-like (conchoidal) fracture patterns. Frequently found in riverbeds, gravel pits, and sedimentary basins.
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