sedimentary
Chert (specifically tan/pink variety)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: tan to pinkish-beige, Luster: dull to waxy, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to pinkish-beige, Luster: dull to waxy, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed from the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or through the precipitation of silica in sedimentary environments. Can form as nodules in limestone or as distinct bedded deposits.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Industrially used in construction aggregate or as a source of silica.
Geological facts
Chert is so durable that it often survives long after the surrounding rock has weathered away. Known as 'flint' when it occurs in chalk or high-quality dark nodules; 'jasper' when it is red/earthy.
Field identification & locations
Identify in the field by its hardness (it will scratch glass and steel), its smooth curved (conchoidal) fracture surfaces, and its fine-grained, non-clastic texture. Found globally in sedimentary basins.
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