sedimentary
Chert (Flint variety)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, black, or tan with a waxy to dull luster; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, black, or tan with a waxy to dull luster
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, black, or tan with a waxy to dull luster; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.65
Formation & geological history
Formed through the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or by chemical precipitation from silica-rich fluids in limestone/chalk beds. Geologically common from the Precambrian to Cenozoic eras.
Uses & applications
Historically used for stone tools (arrowheads, knives) due to sharp edges; currently used as road aggregate, in glass manufacturing, and as a component in ceramics.
Geological facts
Flint is a specific variety of chert often found in chalk. It was one of the most important minerals for early human survival, used both for weaponry and for striking against steel/pyrite to create sparks for fire.
Field identification & locations
Identify in the field by its characteristic smooth, curved (conchoidal) fracture surfaces and its ability to scratch glass easily. Commonly found in nodules within limestone or chalk outcrops and as rounded pebbles in riverbeds.
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