sedimentary
Chert (often called Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, and brown; Luster: Waxy to dull; Crystal structure: Trigonal (cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Gray, white, and brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, and brown; Luster: Waxy to dull; Crystal structure: Trigonal (cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments; age varies from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and weapons; currently used in construction aggregate, as a gemstone (Jasper varieties), and for starting fires (flint and steel).
Geological facts
Chert is so hard it can scratch glass and steel. It was one of the most vital materials for early humans to create sharp-edged tools like arrowheads and scrapers.
Field identification & locations
Identify by its 'shell-like' conchoidal fractures, sharp edges when broken, and waxy texture. Commonly found in limestone or chalk beds as nodules.
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