sedimentary
Chert (White Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: White to off-white with tan weathering; Luster: Waxy to dull; Crystal structure: Cryptocrystalline/Trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- White to off-white with tan weathering
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to off-white with tan weathering; Luster: Waxy to dull; Crystal structure: Cryptocrystalline/Trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through 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 (arrowheads/scrapers) due to sharp edges; currently used in construction aggregate, road surfacing, and as a raw material for ceramics.
Geological facts
Chert is so hard it can scratch steel and was commonly used alongside high-carbon steel to create sparks for starting fires in the form of 'flint and steel'.
Field identification & locations
Identify by its waxy texture and shell-like (conchoidal) fractures. Often found as nodules within limestone or as river-worn cobbles. It will not react with acid, unlike limestone.
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