sedimentary
Chert (Flint variety)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, black, or brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, black, or brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, black, or brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or by chemical precipitation from silica-rich fluids in limestone/chalk beds.
Uses & applications
Historically used for stone tools and weapons due to sharp edges; currently used as a gemstone (lapis-like), in road construction, and for fire-starting strikers.
Geological facts
Flint was the primary material for the Stone Age 'industry'. It produces sparks when struck against steel, which led to its use in flintlock firearms.
Field identification & locations
Identify by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. Commonly found as nodules in limestone or as river pebbles.
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