sedimentary

Flint (Chert nodule)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness 7 on the Mohs scale, dark gray to brownish-gray interior with a characteristic chalky white outer cortex (patina), waxy to dull luster, conchoidal fracture with sharp edges, specific gravity ~2.60–2.65.

Identified November 15, 2026More sedimentary →

Explore Flint (Chert nodule) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed through biochemical precipitation of silica within marine chalk or limestone deposits, typically derived from the dissolution of siliceous sponge spicules or radiolarians during diagenesis (Cretaceous to early Tertiary periods).

Uses & applications

Historically used for prehistoric stone tools (knapping) and fire-starting (flintlock firearms and spark generation). Modern uses include decorative gravel, abrasives, and road building aggregate.

Geological facts

Flint was crucial to the development of human civilization during the Stone Age due to its predictable conchoidal fracturing, allowing early humans to knap extremely sharp cutting edges for weapons and scrapers.

Field identification & locations

Recognized in the field by its dark glassy-to-waxy interior exposed through a soft, weathered chalky exterior cortex; produces sparks when struck sharply against carbon steel. Abundant in chalk formations such as the White Cliffs of Dover, UK, and limestone regions worldwide.