sedimentary
Chert (Limestone-based)
Silicon dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: tan to brown, Luster: waxy to dull, Crystal structure: cryptocrystalline (microscopic), Cleavage: none (conchoidal fracture), Specific gravity: 2.5-2.8
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to brown, Luster: waxy to dull, Crystal structure: cryptocrystalline (microscopic), Cleavage: none (conchoidal fracture), Specific gravity: 2.5-2.8
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by the replacement of calcium carbonate in limestone by silica-rich fluids. Common in many geological ages from Precambrian to recent.
Uses & applications
Historical use for stone tools and arrowheads; currently used as construction aggregate, road base, and decorative landscaping stone.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture allows it to be shaped into razor-sharp edges for hunting and cutting.
Field identification & locations
Identify in the field by its extreme hardness (it will scratch glass and steel), its smooth waxy feel when freshly broken, and its spark when struck against steel. Found globally in nodules within limestone beds.
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