sedimentary
Chert (Flint variety)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Grey, tan, or white; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Grey, tan, or white
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grey, tan, or white; Luster: Waxy to dull; 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 from fluids; typically found as nodules in limestone or chalk beds dating from the Precambrian to the present.
Uses & applications
Historically used for stone tools and arrowheads; currently used in construction aggregate, road surfacing, and as a component in certain ceramics.
Geological facts
Chert was one of the first materials used by early humans to create fire and sharp tools due to its predictable conchoidal fracturing. 'Flint' is technically a high-quality variety of chert found in chalk or marly limestone.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its sharp, shell-like (conchoidal) breaking pattern. It is commonly found in riverbeds or eroded out of limestone outcrops worldwide.
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