sedimentary
Chert (Flint)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 (Mohs scale), Color: tan, brown, or grey (often waxy), Luster: dull to vitreous/waxy, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, brown, or grey (often waxy), Luster: dull to vitreous/waxy, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments; age varies from Precambrian to Holocene.
Uses & applications
Used historically for stone tools and weapons; currently used in construction aggregate, road surfacing, and as a raw material for silicon production.
Geological facts
Chert is known for its ability to produce sparks when struck against steel, making it vital for early fire-starting. It breaks with a sharp, shell-like edge called a conchoidal fracture.
Field identification & locations
Identify by its hardness (cannot be scratched by steel) and smooth, curved fracture surfaces. Commonly found in limestone beds or as river pebbles. Collectors look for colorful variants like Jasper.
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