sedimentary
Chert (and Chert Flake)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Chalky white to light gray; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Chalky white to light gray
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Chalky white to light gray; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed from the precipitation of silica-rich fluids in sedimentary environments, often replacing carbonate rocks or as nodules in limestone/chalk. This specimen appears to be a debitage flake or a primitive lithic tool fragment.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used in road construction, as jewelry (if colorful), and as a starting material for silicon.
Geological facts
Chert has been used by humans for millions of years to create tools. When struck against steel, it can produce sparks, though not as effectively as its variety known as flint.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by steel), smooth conchoidal fracture patterns, and fine texture. Commonly found in limestone outcrops or as river cobbles.
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