sedimentary
Chert (Flint variety)
Chert (SiO2)
Hardness: 7 (Mohs); Color: Tan/Grey; Luster: Dull to waxy; Crystal structure: Microcrystalline (Cryptocrystalline) quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs)
- Color
- Tan/Grey
- Luster
- Dull to waxy
Identified More sedimentary →
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Physical properties
Hardness: 7 (Mohs); Color: Tan/Grey; Luster: Dull to waxy; Crystal structure: Microcrystalline (Cryptocrystalline) quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed from the accumulation of siliceous remains of marine organisms (like diatoms or radiolaria) or by chemical precipitation. This particular specimen appears to be a weathered nodule, possibly from Paleozoic or Mesozoic limestone beds.
Uses & applications
Historically used for stone tools (arrowheads). Modern uses include road surfacing, jewelry (when colorful), and as a raw material in ceramics or glass.
Geological facts
Chert is so hard it can create sparks when struck against steel, leading to its widespread use in flintlock firearms. It was the most important material for early human technology during the Stone Age.
Field identification & locations
Identify by its 'shell-like' conchoidal fracture which leaves sharp edges, its extreme hardness (will scratch glass), and its fine-grained texture. Commonly found in creek beds and limestone outcrops.
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