sedimentary
Chert (Chert / Flint)
Silicon dioxide (SiO2) - Microcrystalline quartz
Hardness: 7 (Mohs scale), Color: Brown, gray, or tan with waxy luster. Crystal structure: Cryptocrystalline. Exhibits conchoidal fracture (smooth, curved breaks) and is very dense.
- Hardness
- 7 (Mohs scale), Color: Brown, gray, or tan with waxy luster
- Color
- Brown, gray, or tan with waxy luster
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Physical properties
Hardness: 7 (Mohs scale), Color: Brown, gray, or tan with waxy luster. Crystal structure: Cryptocrystalline. Exhibits conchoidal fracture (smooth, curved breaks) and is very dense.
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by chemical precipitation from silica-rich fluids within limestone or chalk beds. Often Paleozoic to Mesozoic in age.
Uses & applications
Historically used for stone tools and arrowheads because of its sharp edges. Today used in construction aggregate, road surfacing, and occasionally as a lapidary material for tumbling.
Geological facts
Chert is so hard it can scratch steel. When struck against steel, it can produce sparks, leading to its historical use in flintlock firearms and fire-starting kits.
Field identification & locations
Identify in the field by its waxy appearance and sharp, shell-like (conchoidal) fractures. It will not react with acid like limestone. Common in stream beds and road cuts near sedimentary rock formations.
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