sedimentary
Chert (variations include Flint or Jasper)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: waxy to dull; Crystal structure: Hexagonal (microscopic); Cleavage: none; Fracture: Conchoidal (shell-like curves); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: waxy to dull; Crystal structure: Hexagonal (microscopic); Cleavage: none; Fracture: Conchoidal (shell-like curves); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by the chemical precipitation of silica in groundwater. It is found in geologic strata from the Precambrian to the present, often occurring as nodules or beds within limestone or chalk.
Uses & applications
Historically used for making sharp stone tools and weapons (arrowheads, scrapers). Modern uses include road surfacing, construction aggregate, and occasionally as a gemstone (Jasper) in jewelry. It is also a source of flint for fire-starting.
Geological facts
Chert is so hard it can scratch steel. Because it breaks with a conchoidal fracture like glass, it creates edges that can be sharper than a surgical scalpel. It was one of the most vital materials for prehistoric technology.
Field identification & locations
Identify in the field by its hardness (it should easily scratch glass), its waxy feel, and the distinctive curved 'conchoidal' chips where it has been struck. Commonly found in riverbeds, glacial deposits, and embedded in limestone outcrops.
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