sedimentary

Flint

SiO2 (Cryptocrystalline Quartz / Chert)

Hardness: 7 on Mohs scale; Color: Gray, dark brown, or black with lighter mottling; Luster: Waxy to vitreous; Crystal structure: Microcrystalline/cryptocrystalline quartz (trigonal); Cleavage: None, exhibits conchoidal fracture; Specific gravity: 2.60 to 2.65.

Hardness: 7 on Mohs scale
Color: Gray, dark brown, or black with lighter mottling
Luster: Waxy to vitreous

Identified July 31, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the replacement of calcium carbonate by silica-rich solutions in marine limestone or chalk environments during the Cretaceous and other periods, or through the accumulation of siliceous skeletal remains of marine organisms.

Uses & applications

Historically used for making stone tools, arrowheads, and spark-producing fire starters. Currently used in decorative aggregates, road construction, and occasionally in lapidary work.

Geological facts

Flint has been used by early humans for hundreds of thousands of years to create sharp cutting edges and start fires through percussion against steel or iron pyrites.

Field identification & locations

Easily identified by its distinctive conchoidal fracture, waxy luster, and high hardness that scratches glass. Commonly found weathering out of chalk or limestone deposits globally.