sedimentary

Flint

Microcrystalline quartz (SiO2)

Hardness: 7 on the Mohs scale. Color: Dark gray, black, brown, or dark blue. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline (microscopic quartz crystals). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.6 - 2.65.

Hardness: 7 on the Mohs scale
Color: Dark gray, black, brown, or dark blue
Luster: Waxy to vitreous

Identified August 4, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as nodules or masses in sedimentary rocks, primarily chalk or marine limestones, through the replacement of calcium carbonate by silica-rich solutions over millions of years.

Uses & applications

Historically used for making stone tools, weapons, and fire-starting flintlock mechanisms. Currently used in landscaping, road construction, and occasionally for decorative items.

Geological facts

Flint was one of the most important materials for early humans during the Stone Age due to its ability to be knapped into extremely sharp edges and create sparks when struck against steel.

Field identification & locations

Easily identified by its characteristic smooth, dark exterior, waxy luster, and sharp conchoidal fracture when broken, revealing lighter interiors. Found worldwide in chalk deposits.