sedimentary
Chert (variations include Flint or Jasper)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Brown, tan, or gray; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Brown, tan, or gray
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Brown, tan, or gray; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by chemical precipitation in groundwater that replaces limestone or chalk. Can be found in geological strata ranging from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and weapons (arrowheads); currently used as a raw material in road construction, as a gemstone (jasper varieties), and as fire-starting flint.
Geological facts
Chert is so hard it can scratch glass and steel. Because it breaks with a conchoidal fracture like glass, it creates extremely sharp edges, which is why it was the primary choice for Neolithic tools.
Field identification & locations
Identify in the field by its smooth, waxy feel and the way it breaks into curved, shell-like (conchoidal) shards. Commonly found in riverbeds or as nodules within limestone outcrops globally.
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