sedimentary
Chert (Flint)
Microcrystalline quartz (SiO2)
Hardness of 7 on the Mohs scale, typically white, grey, brown, or tan in color, waxy to dull luster, cryptocrystalline structure with conchoidal fracture, specific gravity of 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, typically white, grey, brown, or tan in color, waxy to dull luster, cryptocrystalline structure with conchoidal fracture, specific gravity of 2.60 to 2.65.
Formation & geological history
Formed through the chemical precipitation of silica from aqueous solutions, often replacing carbonate rocks like limestone during diagenesis. Can range from millions to hundreds of millions of years old.
Uses & applications
Historically used for making stone tools, arrowheads, and spark generation in firearms. Modern uses include abrasives and aggregate.
Geological facts
Chert that is dark grey or black is often called flint. Due to its conchoidal fracture, it breaks into extremely sharp edges, making it ideal for primitive weaponry and tools.
Field identification & locations
Identify by its hardness (scratches glass easily), conchoidal fracture patterns, and waxy luster. Commonly found in limestone and chalk formations worldwide.
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