sedimentary
Chert (including Flint and Jasper variants)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: variety of grays, blacks, and browns; Luster: waxy to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- variety of grays, blacks, and browns
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: variety of grays, blacks, and browns; Luster: waxy to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments; age varies from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and weapons (arrowheads); currently used in road construction, as gemstones when colorful (jasper), and for starting fires (flint).
Geological facts
Chert was one of the most important materials for early humans because its conchoidal fracture creates extremely sharp edges; it is also highly resistant to chemical weathering.
Field identification & locations
Identify in the field by checking for a smooth, glass-like fracture (conchoidal), high hardness (cannot be scratched by a steel knife), and a waxy texture. Commonly found as nodules in limestone or chalk beds.
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