sedimentary

Flint

Silicon Dioxide (SiO2) - Chert variety

Hardness: 7 (Mohs scale), Color: Dark grey to black, Luster: Waxy to vitreous, Structure: Cryptocrystalline, Fracture: Conchoidal (shell-like), Cleavage: None

Identified July 12, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: Dark grey to black, Luster: Waxy to vitreous, Structure: Cryptocrystalline, Fracture: Conchoidal (shell-like), Cleavage: None

Formation & geological history

Formed as nodules or masses in sedimentary rocks like chalk and limestone through the replacement of calcium carbonate by silica in groundwater. Often occurs in Cretaceous deposits.

Uses & applications

Used historically for stone tools (arrowheads, knives) and strike-a-lights for fire starting. Modern uses include road construction, glass manufacturing, and as grinding media in ball mills.

Geological facts

Flint has been used for millions of years; its ability to break with very sharp edges made it the primary material for the Stone Age. It produces sparks when struck against steel due to the friction scraping off tiny particles of iron that ignite in air.

Field identification & locations

Identify by its waxy texture, dark color, and sharp conchoidal fracture edges. Often has a white outer 'rind' (cortex) when found in nature. Common in the UK (Dover), France, and the USA.