sedimentary

Flint

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness of 7 on the Mohs scale, color typically grey, white, brown, or black with a chalky outer cortex, waxy to vitreous luster, conchoidal fracture, and specific gravity of 2.60 to 2.65.

Identified July 29, 2026More sedimentary →

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Physical properties

Hardness of 7 on the Mohs scale, color typically grey, white, brown, or black with a chalky outer cortex, waxy to vitreous luster, conchoidal fracture, and specific gravity of 2.60 to 2.65.

Formation & geological history

Formed as nodules in sedimentary rocks such as chalk and limestone through the replacement of calcium carbonate by silica-rich solutions during the Cretaceous period.

Uses & applications

Historically used for making stone tools, arrowheads, and fire-starting flintlocks; currently used in aggregate, abrasive grit, and decorative landscaping.

Geological facts

Flint produces sparks when struck against steel due to iron particles being shaved off and ignited by the friction, making it crucial for survival and fire-making throughout human history.

Field identification & locations

Easily identified by its conchoidal fracture (smooth, curved breakage surfaces with sharp edges), white chalky cortex rind, and extreme hardness that scratches glass. Commonly found in chalk deposits worldwide, especially along coastal cliffs like the White Cliffs of Dover.