sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Tan to reddish-brown with dark banding, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Tan to reddish-brown with dark banding, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed via the accumulation of siliceous remains of organisms (like diatoms or radiolarians) or through the chemical precipitation of silica in groundwater. Can form as nodules or bedded deposits within limestone or dolomite.
Uses & applications
Used historically for stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Modern uses include road surfacing, decorative landscaping, and occasionally as fire-starting flint.
Geological facts
Because it is harder than steel and breaks with very sharp edges, chert was one of the most vital materials for prehistoric human survival. 'Flint' is a variety of chert typically found in chalk or marly limestone.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), waxy appearance, and smooth, curved (conchoidal) fracture surfaces. Common in limestone outcrops and riverbeds.
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