sedimentary
Chert (Flint variety)
Silicon dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 Mohs scale. Color: Dark brown to black. Luster: Waxy to dull. Crystal Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.
- Hardness
- 7 Mohs scale
- Color
- Dark brown to black
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale. Color: Dark brown to black. Luster: Waxy to dull. Crystal Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.
Formation & geological history
Formed through the replacement of limestone or chalk by silica-rich fluids, or by the accumulation of siliceous skeletal remains of marine organisms like diatoms and radiolarians. Commonly found in Mesozoic Era deposits.
Uses & applications
Historically used for stone tools (arrowheads, knives) due to sharp edges; used today as a decorative stone, in construction aggregates, and occasionally as a gemstone in cabochon form.
Geological facts
Flint was one of the most important minerals for early human development, used both for sparking fires and manufacturing sharp tools. It creates a spark when struck against steel.
Field identification & locations
Identify by its characteristic oyster-shell-like (conchoidal) fracture and sharp edges. Found in nodules within limestone or chalk beds. Often smooth to the touch except where fractured.
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