sedimentary
Chert / Jasper
Microcrystalline Quartz (SiO2)
Mohs hardness 6.5-7; waxy to vitreous luster; microcrystalline/cryptocrystalline structure; no cleavage; sharp conchoidal fracture; variable colors including brownish-red, cream, grey, and purplish tones.
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Physical properties
Mohs hardness 6.5-7; waxy to vitreous luster; microcrystalline/cryptocrystalline structure; no cleavage; sharp conchoidal fracture; variable colors including brownish-red, cream, grey, and purplish tones.
Formation & geological history
Formed through the accumulation and precipitation of silica-rich fluids in sedimentary environments or volcanic ash beds, often during low-grade metamorphism or diagenesis.
Uses & applications
Historically used for knapping stone tools (arrowheads, scrapers) due to its conchoidal fracture; modernly used as tumbled lapidary material, decorative stones, and rock tumbler specimens.
Geological facts
Chert and jasper are among the oldest materials used by early humans for toolmaking. Variations with rich red or patterned banding are highly prized by rockhounds and lapidary artists.
Field identification & locations
Identify in the field by its hardness (scratches glass easily, steel knife cannot scratch it), smooth waxy feel, and smooth curved conchoidal fractures. Commonly found in riverbeds, gravel deposits, and limestone formations globally.
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