sedimentary
Chert (Yellow Jasper/Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Yellow to tan-orange, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Yellow to tan-orange, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed by the precipitation of silica from aqueous fluids, often in marine environments or as groundwater replaces organic material or minerals in limestone. This chemical sedimentary process results in a dense, hard rock.
Uses & applications
Historically used for stone tools and arrowheads. Currently used in jewelry (as yellow jasper), landscape decoration, and as a raw material in road construction.
Geological facts
Yellow chert is often referred to as 'yellow jasper' in the gem trade. Because it strikes sparks against steel, it was essential for flintlock firearms in many parts of the world.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by steel) and smooth, shell-like (conchoidal) breaks. Typically found in gravel beds, riverbanks, or as nodules within limestone formations.
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