sedimentary
Chert (Jasper/Flint variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Brown, grey, and tan banding, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.6-2.65
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Brown, grey, and tan banding, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.6-2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by chemical precipitation from ground fluids replacing limestone or chalk. Commonly found in sedimentary strata ranging from Precambrian to Cenozoic eras.
Uses & applications
Historically used for stone tools (arrowheads/scrapers) due to its sharp conchoidal fracture. Modern uses include road surfacing, decorative stones, and semi-precious jewelry when vibrantly colored.
Geological facts
Chert is so hard it can scratch steel. When struck against steel, it can produce sparks, leading to its historical use in flintlock firearms and for starting fires.
Field identification & locations
Identify by its waxy texture and shell-like (conchoidal) curved fracture patterns. Commonly found in gravel beds, river banks, and as nodules within limestone outcrops.
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