sedimentary
Chert (Brown Variety)
Microcrystalline quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Brown/Tan, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Brown/Tan, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. Can vary in age from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and arrowheads. Currently used as road aggregate, in jewelry as jasper variants, and as a geological indicator.
Geological facts
Chert is so hard it can strike sparks against steel. It was one of the most vital materials for prehistoric technology due to its predictable fracturing pattern.
Field identification & locations
Identify by its 'shell-like' conchoidal fracture, smooth texture, and ability to scratch glass. Found globally in limestone and chalk beds as nodules or layers.
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