sedimentary

Flint (Chert)

Cryptocrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Black, grey, or dark brown; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Black, grey, or dark brown
Luster: Waxy to vitreous

Identified May 18, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Black, grey, or dark brown; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed as nodules in sedimentary rocks such as chalk or limestone. It originates from the accumulation of siliceous skeletal remains (like sponges or diatoms) that dissolve and reprecipitate, often during the Cretaceous period.

Uses & applications

Historically used for stone tools (knapping) and striking fire. Modern uses include abrasives, road construction, and as a decorative stone in landscaping or historic masonry.

Geological facts

Flint was the primary material for human technological advancement during the Stone Age. It produces sparks when struck against steel due to its hardness and friction-induced oxidation.

Field identification & locations

Identify by its characteristic conchoidal (shell-like) fracture edges which are extremely sharp. Common in the UK (Jurassic Coast), France, and the USA. Collectors look for unique nodules or artifacts.