sedimentary
Chert (Flint)
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 Mohs; Color: White, gray, tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 Mohs
- Color
- White, gray, tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs; Color: White, gray, tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed primarily through the chemical precipitation of silica-rich fluids or the accumulation of siliceous remains (like diatoms or radiolaria) in sedimentary basins, often occurring as nodules in limestone or chalk.
Uses & applications
Historically used for stone tools (knapping) and fire-starting; currently used as a decorative stone, in road construction, and for jewelry like cabochons.
Geological facts
Flint is a variety of chert that was essential to prehistoric humans for making arrowheads and spear points due to its sharp, conchoidal fracture edges.
Field identification & locations
Identify by its extreme hardness (scratches glass), waxy luster, and smooth, curved fracture surfaces. Commonly found in limestone outcrops or as river pebbles.
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