sedimentary
Chert Nodule (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Dark gray/black with tan cortex, Luster: Waxy to dull, Crystal Structure: Trigonal/Microcrystalline, Cleavage: None (Conchoidal fracture)
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Physical properties
Hardness: 7 (Mohs scale), Color: Dark gray/black with tan cortex, Luster: Waxy to dull, Crystal Structure: Trigonal/Microcrystalline, Cleavage: None (Conchoidal fracture)
Formation & geological history
Formed by the accumulation of silica-rich fluids within limestone or chalk beds. As the silica replaces carbonate minerals, it creates nodules. Common in Cretaceous and Paleozoic marine deposits.
Uses & applications
Historically used for stone tools and starting fires; currently used as a raw material for ceramics, decorative garden stone, and collected as specimens.
Geological facts
Flint was arguably the first 'industrial' rock of humanity, used to create arrowheads and knives. It produces sparks when struck against steel due to its hardness and sharp edges.
Field identification & locations
Identified by its extremely smooth, shell-like fracture pattern (conchoidal) and its ability to scratch glass. Often found in riverbeds or weathered out of chalk cliffs.
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