sedimentary
Chert (and Jasper) Nodules in Limestone
Silicon Dioxide (SiO2) microcrystalline quartz
Hardness: 7 (Mohs scale), Color: Brownish-red (Jasper) with greyish-blue (Chert) interior, Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture)
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Physical properties
Hardness: 7 (Mohs scale), Color: Brownish-red (Jasper) with greyish-blue (Chert) interior, Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture)
Formation & geological history
Formed through the accumulation of silica-rich fluids within sedimentary rock layers, often replacing carbonate material or filling voids in limestone. This process typically occurs in marine environments over millions of years.
Uses & applications
Historically used for making stone tools (flint knapping) due to its sharp edges; used today as a decorative stone, in lapidary work, and sometimes as an abrasive.
Geological facts
Chert and its red variety, Jasper, have been used by humans for hundreds of thousands of years to create arrowheads and scrapers because they break with predictable, razor-sharp conchoidal fractures.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a steel knife) and its smooth, shell-like fracture pattern. Often found as nodules or layers within limestone or chalk beds.
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