sedimentary
Chert (often called Flint or Chalcedony Jasper)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: typically tan, brown, or pinkish with waxy/dull luster; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- typically tan, brown, or pinkish with waxy/dull luster
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Physical properties
Hardness: 7 on Mohs scale; Color: typically tan, brown, or pinkish with waxy/dull luster; Crystal structure: Trigonal (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 chemical precipitation in marine environments; age can range from Precambrian to Holocene.
Uses & applications
Historically used for stone tools (arrowheads and scrapers) due to its sharp conchoidal fracture. Modernly used as road surface material, in construction aggregate, and occasionally as semi-precious gemstones for jewelry.
Geological facts
Chert is so hard it can scratch steel and glass. It was one of the most vital materials for early humans to create fire-starting kits and weaponry. Some varieties, like 'Novaculite', are highly prized as whetstones for sharpening blades.
Field identification & locations
Identify in the field by its characteristic 'shell-like' (conchoidal) fracture patterns and ability to scratch common glass. It is commonly found as nodules in limestone or chalk beds globally, specifically in regions like the Missouri Ozarks or the English Chalk.
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