sedimentary
Chert
Microcrystalline quartz (SiO2)
Hardness of 7 on the Mohs scale, colors vary from white to gray, brown, and black, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture, specific gravity of 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, colors vary from white to gray, brown, and black, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture, specific gravity of 2.60 to 2.65.
Formation & geological history
Formed through the chemical precipitation of silica from aqueous solutions or the accumulation of siliceous skeletal remains of microscopic organisms like radiolarians and diatoms, typically during the Cretaceous and other geological periods in marine environments.
Uses & applications
Historically used for making stone tools, arrowheads, and fire starters due to its conchoidal fracture. Today occasionally used in decorative landscaping, road aggregate, and sometimes in lapidary arts.
Geological facts
Chert is a durable sedimentary rock that weathers very slowly, often remaining as resistant gravel in stream beds. Varieties like flint and jasper are well-known types of chert.
Field identification & locations
Can be identified in the field by its hard, dense nature, waxy luster, and sharp conchoidal fracture edges. Commonly found within limestone formations worldwide.
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