sedimentary
Chert / Flint
Microcrystalline or cryptocrystalline quartz (SiO2)
Hardness: 7 on Mohs scale; Color: typically grey, brown, or tan; Luster: waxy to dull; Crystal structure: hexagonal (microscopic); Cleavage: none (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- typically grey, brown, or tan
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically grey, brown, or tan; Luster: waxy to dull; Crystal structure: hexagonal (microscopic); Cleavage: none (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed via the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from fluids within limestone or chalk beds. Can range from Precambrian to Holocene in age.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) and starting fires. Modern uses include road surfacing, glass manufacturing, and as gemstones in the case of colorful varieties like jasper.
Geological facts
A key characteristic of chert is its 'conchoidal fracture,' which creates sharp edges similar to glass. It was one of the most important stone materials for prehistoric humans globally.
Field identification & locations
Identify by its waxy texture and shell-like (conchoidal) curved fracture patterns when broken. Found commonly in limestone outcrops or as river pebbles. Collectors look for unique banding or historical tool shaping.
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