sedimentary
Chert (Flint)
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 (Mohs scale), Color: White to grey/blueish, Luster: Waxy or dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6
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Physical properties
Hardness: 7 (Mohs scale), Color: White to grey/blueish, Luster: Waxy or dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6
Formation & geological history
Formed primarily through the chemical precipitation of silica-rich fluids within sedimentary rock layers, often replacing limestone or forming as nodules. It commonly develops in deep-sea environments from siliceous organisms like radiolaria or diatoms.
Uses & applications
Historically used for stone tools and weapons (arrowheads) due to its sharp edges. Modernly used as road aggregate, in glass manufacturing, and as a flint-and-steel fire starter.
Geological facts
Because it breaks with a conchoidal fracture (curved, glass-like surfaces), it was one of the most important minerals for prehistoric humans to create cutting tools. It is virtually indestructible by weathering.
Field identification & locations
Identify in the field by its waxy luster, hardness (it will scratch glass), and its characteristic shell-like (conchoidal) fracture pattern. Commonly found in limestone or chalk beds worldwide.
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