sedimentary
Chert
Silicon Dioxide (SiO2)
Hardness of 7 on the Mohs scale, typically brown, gray, or black in color, waxy to vitreous luster, microcrystalline to cryptocrystalline quartz structure, conchoidal fracture with no true cleavage, specific gravity of around 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, typically brown, gray, or black in color, waxy to vitreous luster, microcrystalline to cryptocrystalline quartz structure, conchoidal fracture with no true cleavage, specific gravity of around 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 in deep marine environments over millions of years.
Uses & applications
Historically used extensively by ancient humans for making stone tools, arrowheads, and blades due to its sharp conchoidal fracture. Also used historically for striking fire with steel.
Geological facts
Chert is a tough, weathering-resistant rock that often occurs as nodules, concretionary masses, or layered deposits within sedimentary rocks like limestone and chalk.
Field identification & locations
Identify in the field by its extreme hardness (scratches glass easily), waxy luster, and characteristic conchoidal fracture. Commonly found globally in limestone and chalk formations.
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