sedimentary
Chert (Jasper/River Stone)
Silicon dioxide (SiO2) - Microcrystalline quartz
Hardness: 6.5-7 (Mohs); Color: Brown, grey, tan with slight veining; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Brown, grey, tan with slight veining
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Brown, grey, tan with slight veining; Luster: Dull to waxy; 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 through the chemical precipitation of silica in groundwater. This specimen has been water-worn into a smooth river cobble.
Uses & applications
Historically used for stone tools due to sharp edges; currently used for decorative landscaping, gravel, and occasionally as lapidary material for polishing.
Geological facts
Chert was one of the most important materials for early humans to create arrowheads and scrapers. It can range in color from white to black depending on impurities like iron or organic carbon.
Field identification & locations
Identify by its hardness (will scratch glass) and its smooth, rounded river-worn texture. Common in riverbeds, glacial till, and sedimentary basins worldwide.
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