sedimentary
Chert (Commonly known as Flint or Jasper when pigmented)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, white, or light brown (as seen in specimen); Luster: Waxy to dull; Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, white, or light brown (as seen in specimen)
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, white, or light brown (as seen in specimen); Luster: Waxy to dull; Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in marine environments. It often forms as nodules in limestone or chalk beds and can range from Precambrian to Holocene in age.
Uses & applications
Historically used for stone tools and weapons due to sharp edges; currently used as road aggregate, in glass manufacturing, and occasionally as semi-precious gemstones or decorative landscaping rocks.
Geological facts
Chert was one of the most important resources for prehistoric humans because it breaks with a conchoidal fracture, creating razor-sharp edges for arrowheads and scrapers. It can even create sparks when struck against steel.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like fracture pattern. It is commonly found globally in sedimentary basins, riverbeds, and as nodules in limestone outcrops.
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