sedimentary
Chert / Flint
Silicon dioxide (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Gray, black, tan, or brown; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 6
- Color
- Gray, black, tan, or brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Gray, black, tan, or brown; 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 like diatoms and radiolarians, or through chemical precipitation in marine or groundwater environments. Found throughout almost all geological ages.
Uses & applications
Historically used for stone tools (knapping) and fire-starting. Currently used in road surfacing, as grinding media in ball mills, and occasionally in jewelry as tumble-polished stones.
Geological facts
Flint is a variety of chert. When struck against steel, chert particles break off and oxidize to create sparks, making it essential for ancient survival and early firearms like flintlocks.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture pattern. Commonly found in limestone or chalk beds and as rounded pebbles on beaches.
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