sedimentary

Flint

SiO2 (Microcrystalline quartz / Chert)

Hardness: 7 on the Mohs scale. Color: Dark grey, black, brown, or white. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline / Microcrystalline quartz (chalcedony). Cleavage: None, exhibits conchoidal fracture.

Hardness: 7 on the Mohs scale
Color: Dark grey, black, brown, or white
Luster: Waxy to vitreous

Identified July 31, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the chemical replacement of calcium carbonate in limestone or chalk by silica-rich solutions originating from sponge spicules or dissolved siliceous oozes, generally during the Cretaceous period.

Uses & applications

Historically used for making stone tools, arrowheads, and firearm ignition mechanisms (flintlocks). Currently used in decorative stone work, grinding pebbles, and abrasive products.

Geological facts

Flint is a hard, sedimentary form of quartz that produces a spark when struck against steel, making it historically crucial for starting fires.

Field identification & locations

Identified by its conchoidal fracture (smooth, curved breakage resembling shell impressions), waxy luster, and ability to scratch glass easily. Commonly found embedded in chalk or limestone formations worldwide.