sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Dark brown to black; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Dark brown to black
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Dark brown to black; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed as nodules or beds in sedimentary rocks through the precipitation of silica-rich fluids, often from the remains of diatoms or sponges. Found throughout various geological ages from the Precambrian to Cenozoic.
Uses & applications
Used historically for stone tools and fire-starting; currently used in construction aggregate, road surfacing, and as a decorative stone in collecting.
Geological facts
Flint was one of the first materials used by early humans to create arrowheads and scrapers due to its predictable conchoidal fracture which creates razor-sharp edges.
Field identification & locations
Identify by its 'shell-like' conchoidal fracture patterns and inability to be scratched by a steel knife. Frequently found in limestone or chalk beds.
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