sedimentary
Chert (Flint)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 Mohs; Color: Brown, grey, tan, or black; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 Mohs
- Color
- Brown, grey, tan, or black
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 Mohs; Color: Brown, grey, tan, or black; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of siliceous remains of marine organisms (diatoms, radiolarians) or by chemicals precipitating from groundwater in limestone or chalk beds.
Uses & applications
Historically used for stone tools and starting fires; modernly used in road construction, jewelry (as jasper/agate), and sometimes as a chemical flux.
Geological facts
Flint is a variety of chert that occurs in chalk or marly limestone. It was the primary material for prehistoric toolmaking due to its predictable conchoidal fracture which creates sharp edges.
Field identification & locations
Identify by its waxy appearance and sharp, curved (shell-like) fracture edges. Commonly found as nodules within limestone or as river pebbles. Key indicator of prehistoric human activity if found in knapped shapes.
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