sedimentary
Chert (Green Jasperiod)
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 (Mohs), Color: Sage green, grey, and reddish-brown, 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), Color: Sage green, grey, and reddish-brown, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. Often found as nodules in limestone or as bedded deposits.
Uses & applications
Historically used for stone tools (arrowheads) due to sharp edges; currently used as landscaping stone, fill material, and occasionally for lapidary work / cabochons if the color is vibrant.
Geological facts
Chert was one of the first materials used by early humans for tools because it breaks with incredibly sharp edges. Jasper is essentially an opaque variety of chert colored by iron and other impurities.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel nail) and characteristic curved, shell-like (conchoidal) fracture pattern. Commonly found in stream beds and coastal outcrops.
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