sedimentary
Chert
Microcrystalline quartz (SiO2)
Hardness: 7 on Mohs scale, Color: brownish, gray, or tan, Luster: waxy to dull, Crystal structure: microcrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.60 to 2.65
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Physical properties
Hardness: 7 on Mohs scale, Color: brownish, gray, or tan, Luster: waxy to dull, Crystal structure: microcrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 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 marine organisms such as radiolarians and diatoms, over millions of years in marine environments.
Uses & applications
Historically used for making stone tools, arrowheads, and blades due to its sharp conchoidal fracture. Occasionally used in decorative landscaping or lapidary work.
Geological facts
Chert has been utilized by humans for stone tools since the Paleolithic era because it can be chipped to form extremely sharp edges. Flint is a well-known variety of chert.
Field identification & locations
Can be identified in the field by its hardness (scratches glass), waxy luster, and characteristic conchoidal fracture. Commonly found within limestone and chalk formations worldwide.
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