sedimentary
Chert Pebble
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, brown, and reddish-tan; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, brown, and reddish-tan
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, brown, and reddish-tan; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from groundwater within sedimentary rock layers like limestone. This specific specimen has been water-worn and rounded in a high-energy environment like a river or beach.
Uses & applications
Historically used for stone tools and starting fires (flint). Currently used as decorative gravel, in jewelry (when polished), and for road construction ballast.
Geological facts
Chert is so durable that it often survives long after the surrounding rock has eroded away. The reddish hues in this specimen are likely caused by iron oxide (limonite or hematite) impurities.
Field identification & locations
Identify in the field by its hardness (will scratch glass), smooth waxy texture when broken, and conchoidal (shell-like) fracture patterns. Frequently found in riverbeds and glacial tills globally.
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