sedimentary
Chert (Jasper/Quartzite variety)
Microcrystalline Silica (SiO2)
Hardness: 6.5–7 on Mohs scale. Color: Tan, brown, and yellowish-orange. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 6
- Color
- Tan, brown, and yellowish-orange
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5–7 on Mohs scale. Color: Tan, brown, and yellowish-orange. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms) or by chemical precipitation from groundwater within sedimentary rock layers like limestone. These specimens appear to be stream-rounded and weathered.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges; modernly used in road construction, landscaping, and as a low-cost lapidary material for tumbling.
Geological facts
Chert is so durable that it often survives long after its parent rock has eroded away. Native Americans used this specific type of river-worn silica for arrowheads and scrapers because of its predictable fracture pattern.
Field identification & locations
Identify by its 'waxy' smoothness compared to surrounding rocks and its inability to be scratched by a steel knife. Commonly found in riverbeds, glacial till, and gravel pits.
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