sedimentary

Chert (Flint variety)

Silicon dioxide (SiO2) - Microcrystalline Quartz

AI-generated identification · may be incorrect

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

Identified June 22, 2026More sedimentary →

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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.