sedimentary
Chert (variations include Flint/Jasper)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, or black with shell-like (conchoidal) fracture; Luster: Dull to waxy; Crystal structure: Hexagonal (microscopic); Cleavage: None; Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, or black with shell-like (conchoidal) fracture
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, or black with shell-like (conchoidal) fracture; Luster: Dull to waxy; Crystal structure: Hexagonal (microscopic); Cleavage: None; Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by chemical precipitation from groundwater within limestone or chalk beds. It can date from the Precambrian to Cenozoic eras.
Uses & applications
Historically used for making stone tools (arrowheads and scrapers) due to its sharp edges; used today as a road aggregate, in glass manufacturing, and as a component in jewelry (Jasper/Agate varieties).
Geological facts
Chert was one of the most important minerals for early humans because of its ability to produce extremely sharp, durable edges. When struck against steel, it can produce sparks, leading to its historical use in flintlock firearms.
Field identification & locations
Identify in the field by its hardness (will scratch glass), conchoidal fracture (curved, glass-like breaks), and waxy texture. Commonly found as nodules or layers within sedimentary limestone or dolostone formations.
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