sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: Gray, tan, brown, or black, Luster: Waxy to vitreous, Structure: Microcrystalline/Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Gray, tan, brown, or black, Luster: Waxy to vitreous, Structure: Microcrystalline/Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or by chemical precipitation from groundwater within limestone or chalk beds. Most common in Paleozoic to Mesozoic strata.
Uses & applications
Historically used for stone tools and weapons (arrowheads). Modern uses include road surfacing, jewelry (jasper/agate varieties), and fire-starting flint-and-steel kits.
Geological facts
Flint is a variety of chert that occurs in chalk or marly limestone. It was the most important material for human survival during the Stone Age due to its ability to hold a sharp edge.
Field identification & locations
Identify by its extremely smooth, waxy feel and signature bowl-shaped (conchoidal) fractures. Often found as nodules within limestone or as pebbles in riverbeds. It will scratch glass easily.
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