sedimentary
Chert Nodule
Chert (SiO2)
Hardness: 7 (Mohs scale), Color: tan to creamy white interior, Luster: waxy to dull, Crystal structure: microcrystalline/cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to creamy white interior, Luster: waxy to dull, Crystal structure: microcrystalline/cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed via the precipitation of silica in sedimentary environments, often replacing carbonate material or filling voids in limestone layers. Usually Paleozoic to Cenozoic in age depending on the local strata.
Uses & applications
Historically used for making stone tools due to its sharp edges; currently used for construction aggregate, some decorative gardening, and as a geological study specimen.
Geological facts
Chert is essentially the same material as flint, but the term 'flint' is more commonly reserved for dark-colored specimens found in chalk. It breaks with a distinctive conchoidal shell-like fracture pattern.
Field identification & locations
Identifiable by its smooth, waxy interior when broken against a rough, weather-worn tan exterior. Common in riverbeds and limestone outcrops. It will easily scratch glass.
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