sedimentary
Chert (Yellow Jasper variant)
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: translucent yellow to tan, Luster: waxy to dull, Crystal structure: Trigonal (microscopic), Cleavage: None (conchoidal fracture), Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: translucent yellow to tan, Luster: waxy to dull, Crystal structure: Trigonal (microscopic), Cleavage: None (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed via the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments. It can occur across many geological ages from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools/arrowheads due to sharp edges; currently used for decorative stone, lapidary jewelry, and landscaping. High silica content makes it useful in some industrial abrasives.
Geological facts
Chert is so durable that it often survives intense weathering that destroys surrounding rocks. It was one of the most vital materials for early humans because its conchoidal fracture allows it to be knapped into extremely sharp tools.
Field identification & locations
Identify in the field by its waxy luster and smooth, curved (conchoidal) fracture surfaces that resemble broken glass. Found globally in limestone beds or as nodules and pebbles in riverbeds. It cannot be scratched by a steel knife.
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