sedimentary
Chert (Jasper)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs); Color: Reddish-brown, grey, tan; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); SG: 2.6-2.7.
- Hardness
- 6
- Color
- Reddish-brown, grey, tan
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Reddish-brown, grey, tan; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); SG: 2.6-2.7.
Formation & geological history
Formed through the accumulation of silica-rich marine organisms or chemical precipitation from hydrothermal fluids in sedimentary basins. This specimen appears water-worn, potentially from a riverbed or coastal environment.
Uses & applications
Historically used for stone tools due to sharp edges; currently used for landscaping, decorative gravel, and lapidary work (polishing and cabochons).
Geological facts
Chert was a primary resource for early humans to create arrowheads and scrapers. Red varieties are often called Jasper and are valued as semi-precious gemstones.
Field identification & locations
Identify by its hardness (scratches steel), smooth waxy feel when wet, and curved 'clamshell-like' fractures. Commonly found in gravel pits and beaches worldwide.
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