sedimentary
Chert Nodules
Chert (Silicon Dioxide, SiO2)
Hardness: 6.5-7 on Mohs scale. Color: White, gray, or tan. Luster: Waxy to dull. Crystal structure: Cryptocrystalline (microscopic quartz). Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- White, gray, or tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: White, gray, or tan. Luster: Waxy to dull. Crystal structure: Cryptocrystalline (microscopic quartz). Cleavage: None (conchoidal fracture).
Formation & geological history
Formed in sedimentary rocks like limestone or chalk through the replacement of calcium carbonate by silica-rich fluids, often originating from the remains of diatoms or radiolarians.
Uses & applications
Historically used for making stone tools (arrowheads). Currently used as an abrasive, in road construction, and as a landscaping material.
Geological facts
This specimen appears to be a chert or flint nodule. Chert is so hard it can scratch steel and was essential for ancient humans to create sharp cutting edges.
Field identification & locations
Identify by its smooth, waxy surface and characteristic shell-like (conchoidal) fractures where it has been chipped. Commonly found within limestone beds.
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