sedimentary
Chert
Microcrystalline quartz (SiO2)
Hardness of 7 on the Mohs scale, typically green, grey, brown, or black in color, waxy to dull luster, cryptocrystalline structure, conchoidal fracture with no true cleavage, specific gravity around 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, typically green, grey, brown, or black in color, waxy to dull luster, cryptocrystalline structure, conchoidal fracture with no true cleavage, specific gravity around 2.60 to 2.65.
Formation & geological history
Formed by the chemical precipitation of silica from aqueous solutions, or the replacement of limestone by silica-rich fluids during diagenesis. Can range in geological age from Precambrian to recent.
Uses & applications
Historically used by ancient humans for making stone tools, arrowheads, and blades due to its conchoidal fracture. Occasionally used for decorative landscaping or lapidary purposes.
Geological facts
Chert is extremely durable and weather-resistant, which is why ancient stone tools made from it survive well in the archaeological record. Varieties of chert include flint and jasper.
Field identification & locations
Can be identified in the field by its hard, dense nature, waxy luster, and distinctive conchoidal fracture surfaces that resemble broken glass. Found worldwide in sedimentary rock sequences, particularly alongside limestone and chalk formations.
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