sedimentary
Chert (Flint variety)
Chert (SiO2)
Hardness: 6.5-7 (Mohs), Color: Dark grey, brown, tan; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 6
- Color
- Dark grey, brown, tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs), Color: Dark grey, brown, tan; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed by the accumulation of siliceous remains of organisms (radiolarians, diatoms) or by chemical precipitation. This water-worn specimen likely originated in marine sedimentary beds before undergoing alluvial transport and weathering.
Uses & applications
Historically used for stone tools (knapping) and sparking fire. In industry, used as grinding media and in road construction. Smaller tumbled pieces are popular for terrariums and beginner rock collections.
Geological facts
Flint was one of the most vital materials for early humans, used for making arrowheads and hand axes. It exhibits a conchoidal fracture, creating sharp edges even on small fragments.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel), waxy surface, and smooth, curved fracture surfaces. Commonly found along riverbeds, beaches, and in limestone outcrops.
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