sedimentary
Chert / Flint
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs), Color: brown to dark grey, Luster: waxy to dull, Crystal structure: cryptocrystalline, Fracture: conchoidal, Specific gravity: 2.65
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs), Color: brown to dark grey, Luster: waxy to dull, Crystal structure: cryptocrystalline, Fracture: conchoidal, Specific gravity: 2.65
Formation & geological history
Formed from the accumulation of microscopic silica-rich plankton or through the chemical replacement of calcium carbonate in sedimentary layers, often limestone or chalk.
Uses & applications
Historically used for stone tools and starting fires; currently used as a road aggregate, in landscaping, and for knapping by enthusiasts.
Geological facts
Flint is a variety of chert. Because it breaks with a conchoidal fracture, it creates edges sharper than a surgeon's steel scalpel.
Field identification & locations
Identify by its waxy texture and sharp, shell-like edges when broken. Commonly found as nodules in chalk or limestone beds and inside river gravels.
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