sedimentary
Banded Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan, grey, beige, 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: tan, grey, beige, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed through the precipitation of silica from seawater or the replacement of limestone by silica-rich fluids. Common in Precambrian to Cenozoic marine environments, often as nodules or bedded layers.
Uses & applications
Historically used for stone tools (arrowheads and scrapers) due to its sharp conchoidal fracture. Modern uses include abrasives, road construction aggregate, and lapidary work for jewelry.
Geological facts
Also known as flint when found in chalk; banded varieties are often precursors to agates. Chert is extremely durable and often survives long-distance transport in rivers and glacial till.
Field identification & locations
Identify by its 'rings' or bands, extreme hardness (it will scratch glass), and smooth, waxy texture. Commonly found in riverbeds, glacial moraines, and outcrops of sedimentary rock.
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