sedimentary
Chert (varieties include Flint and Jasper)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 (Mohs scale); Color: Variegated beige, tan, and gray; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Variegated beige, tan, and gray
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Variegated beige, tan, and gray; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed from the accumulation of silica-rich organic remains such as radiolaria or diatoms on the seafloor, or through chemical precipitation in limestone. Can range from Precambrian to modern in age.
Uses & applications
Historically used for stone tools and arrowheads; currently used in construction aggregate, road surfacing, and as a raw material for fire-starting strikers.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture creates razor-sharp edges. It is famous for being used as flint in lighters and early firearms.
Field identification & locations
Identify in the field by its extreme hardness (scratches glass) and smooth, curved shell-like (conchoidal) fracture pattern. Commonly found in riverbeds, limestone outcrops, and coastal cliffs.
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