sedimentary
Chert (Flint Nodules)
Microcrystalline quartz (SiO2)
Hardness: 7 Mohs; Color: Gray, tan, white, or black; Luster: Waxy to dull; Structure: Cryptocrystalline; Fracture: Conchoidal (shell-like curves)
- Hardness
- 7 Mohs
- Color
- Gray, tan, white, or black
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs; Color: Gray, tan, white, or black; Luster: Waxy to dull; Structure: Cryptocrystalline; Fracture: Conchoidal (shell-like curves)
Formation & geological history
Formed through chemical precipitation from silica-rich fluids in sedimentary environments, often replacing carbonate material in limestone or chalk during diagenesis.
Uses & applications
Historically used for stone tools and starting fires; currently used for road base, decorative landscaping, and occasionally as a source for high-purity silica.
Geological facts
Because it breaks with a conchoidal fracture like glass, it produces very sharp edges, which is why it was the primary material for prehistoric arrowheads and scrapers.
Field identification & locations
Identify by its extreme hardness (scratches glass), waxy appearance, and the way it breaks into sharp, curved flakes. Common in limestone outcrops.
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