sedimentary
Chert (variations include Flint or Jasper)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: dull gray to greenish-gray, Luster: waxy to dull, Crystal structure: Trigonal (microscopic), Cleavage: none (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: dull gray to greenish-gray, Luster: waxy to dull, Crystal structure: Trigonal (microscopic), 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 from groundwater within sedimentary beds. Found in limestone or chalk deposits throughout many geological eras from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and weapons (arrowheads) due to sharp edges; currently used as a raw material for concrete, road surfacing, and as a polishing abrasive.
Geological facts
Chert was one of the first materials used by prehistoric humans to make fire and sharp-edged tools. Its conchoidal fracture allows it to break into predictable, razor-sharp pieces.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds or as nodules within limestone outcrops.
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