sedimentary
Chert (Jasper/Chalcedony)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Tan, yellowish-brown, opaque. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Tan, yellowish-brown, opaque
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Tan, yellowish-brown, opaque. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from groundwater within limestone or chalk beds. Often Cretaceous to Paleozoic in age.
Uses & applications
Historically used for stone tools and arrowheads due to sharp edges when fractured. Currently used for gravel, road surfacing, decorative landscaping, and occasionally lapidary work.
Geological facts
Chert and its varieties like flint and jasper were the primary materials for human technology for millions of years. This specimen shows significant river-rounding or water-wear, giving it a smooth, pebble-like texture.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its waxy appearance. Look for conchoidal (shell-like) fractures on broken edges. Common in riverbeds and limestone outcrops.
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