sedimentary
Chert (Flint)
Chert (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Gray, tan, white, or black; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 6
- Color
- Gray, tan, white, or black
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Gray, tan, white, or black; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in marine environments. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools and starting fires; currently used in construction aggregate, road surfacing, and as a low-cost gemstone for lapidary work.
Geological facts
Flint is a variety of chert that was essential to prehistoric humans for crafting sharp-edged arrowheads and knives due to its predictable conchoidal fracturing.
Field identification & locations
Identify by its 'shell-like' curved fractures and ability to scratch glass. Commonly found in gravel pits, stream beds, and limestone outcrops. High-quality colorful pieces are prized by flintknappers.
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