sedimentary
Chert (Yellow Jasper variant)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Yellow-orange to buttery tan, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Yellow-orange to buttery tan, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific gravity: 2.6-2.7
Formation & geological history
Formed from the accumulation of microscopic silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from hydrothermal fluids in sedimentary environments. Often found as nodules within limestone or chalk.
Uses & applications
Historically used for stone tools due to sharp edges when fractured; modernly used for lapidary work, jewelry (as yellow jasper), and as an indicator of sedimentary environments for geologists.
Geological facts
This specific buttery yellow color is often referred to as 'butter jasper' or yellow chert. It is extremely durable and can survive long-distance transport in river beds.
Field identification & locations
Identify in the field by its waxy luster and smooth, shell-like (conchoidal) fracture surfaces. It will easily scratch glass but cannot be scratched by a steel knife. Common in diverse geological settings worldwide.
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