sedimentary
Chert (specifically Flint)
Chert (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, white, and grey banding; Luster: Dull to waxy; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, white, and grey banding
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, white, and grey banding; Luster: Dull to waxy; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed by the precipitation of silica in sedimentary environments, often replacing calcium carbonate in limestone or chalk beds. Formed throughout geological time from the Precambrian to the present.
Uses & applications
Historically used for stone tools (knapping) and fire-starting (flint and steel). Modern uses include road surfacing, jewelry (as semi-precious gemstones), and historical reconstructions.
Geological facts
Chert has a conchoidal fracture, which means it breaks like glass with sharp edges. This made it the premier material for arrowheads and spear points for prehistoric humans.
Field identification & locations
Identify in the field by its hardness (scratches steel), smooth waxy feel on broken surfaces, and distinct curved fracture patterns. Often found in nodules within limestone formations or as stream-worn cobbles.
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