sedimentary
Chert
Cryptocrystalline Quartz (SiO2)
AI-generated identification · may be incorrectHardness: 7 (Mohs), Color: Brown/Grey/Tan, Luster: Dull to waxy, Crystal Structure: Trigonal/Microcrystalline, Cleavage: None/Conchoidal fracture, Specific Gravity: 2.6
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Physical properties
Hardness: 7 (Mohs), Color: Brown/Grey/Tan, Luster: Dull to waxy, Crystal Structure: Trigonal/Microcrystalline, Cleavage: None/Conchoidal fracture, Specific Gravity: 2.6
Formation & geological history
Formed in marine environments through the accumulation of silica-rich organic remains or chemical precipitation. It can be found in sediment layers ranging from various geological ages.
Uses & applications
Historically used for making stone tools (arrowheads). Today used as construction aggregate, in some jewelry as beads, and for sparks in flintlock mechanisms.
Geological facts
Chert is so hard it can scratch glass and steel. It breaks with a sharp, shell-like (conchoidal) fracture, which is why it was prized by prehistoric humans for sharp tools.
Field identification & locations
Identify in the field by its hardness and distinctive waxy texture. It is commonly found in limestone or dolomite beds as nodules or layers. Known globally, with significant deposits in the USA and Europe.
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