sedimentary
Chert / Flint
Microcrystalline Quartz (SiO2)
Hardness 7 on Mohs scale; color ranges from grayish-green to tan with dark inclusions; waxy to dull luster; microcrystalline/cryptocrystalline texture; prominent conchoidal fracture with sharp edges; specific gravity approx. 2.65.
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Physical properties
Hardness 7 on Mohs scale; color ranges from grayish-green to tan with dark inclusions; waxy to dull luster; microcrystalline/cryptocrystalline texture; prominent conchoidal fracture with sharp edges; specific gravity approx. 2.65.
Formation & geological history
Formed in marine environment sediments through the accumulation of siliceous organism remains (like radiolarians or diatoms) or by chemical precipitation, which later undergoes diagenesis.
Uses & applications
Historically used for making stone tools (arrowheads, axes) due to its sharp conchoidal fracture and spark generation with steel; used today in road construction, decor, and flintlock firearms.
Geological facts
Chert has been used by humans for hundreds of thousands of years to craft edge tools. When struck against iron or pyrite, it produces hot sparks capable of lighting fires.
Field identification & locations
Identified by its extreme hardness (scratches glass readily), smooth shell-like (conchoidal) fracture surfaces, and sharp edges. Common in limestone deposits, riverbeds, and gravel pits worldwide.
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