sedimentary
Chert (specifically White Chert or Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Cream, white, or light beige; Luster: Waxy to dull; Crystal structure: Hexagonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Cream, white, or light beige
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Cream, white, or light beige; Luster: Waxy to dull; Crystal structure: Hexagonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by chemical precipitation in marine environments. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools and weapons due to sharp edges; currently used for road surfacing, as an abrasive, and in some jewelry or lapidary work.
Geological facts
Chert was one of the most important materials for early humans because its conchoidal fracture allows it to be shaped into razor-sharp blades. It can also produce sparks when struck against steel.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Common in riverbeds and limestone outcrops.
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