sedimentary
Chert (Jasper/Flint variety)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Reddish-brown, tan, and cream-colored; Luster: Waxy to dull; Crystal structure: Hexagonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Reddish-brown, tan, and cream-colored
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Reddish-brown, tan, and cream-colored; Luster: Waxy to dull; Crystal structure: Hexagonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the precipitation of silica-rich fluids in sedimentary environments (often replacing limestone) or from the accumulation of siliceous remains of microorganisms like diatoms or radiolaria. Originates across various geological ages from Precambrian to Cenozoic.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to conchoidal fracture. Modernly used in jewelry (as jasper), as gemstone cabochons, road surfacing, and as flint for fire-starting.
Geological facts
Chert is so hard it can scratch steel and glass. Red varieties containing iron oxide are commonly called Jasper. It was one of the most vital materials for prehistoric humans globally.
Field identification & locations
Identify by its waxy appearance, extreme hardness, and sharp, shell-like (conchoidal) fracture edges. Commonly found in stream beds, gravel deposits, and as nodules within limestone outcrops. It is nearly ubiquitous in many geological settings.
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