sedimentary

Flint

Microcrystalline quartz (SiO2)

Hardness: 7 on the Mohs scale. Color: Gray, brown, black, or yellowish. Luster: Vitreous to waxy. Crystal structure: Cryptocrystalline (microscopic quartz crystals). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.60-2.65.

Hardness: 7 on the Mohs scale
Color: Gray, brown, black, or yellowish
Luster: Vitreous to waxy

Identified August 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the chemical replacement of calcium carbonate in limestone or chalk by silica-rich solutions during the diagenesis of sedimentary rocks. Typically Cretaceous in age.

Uses & applications

Historically used for making stone tools, weapons, and fire-starting (flint and steel). Currently used in decorative landscaping, construction aggregate, and occasionally in lapidary work.

Geological facts

Flint and chert are essentially the same material, though 'flint' typically refers specifically to the nodules found in chalk deposits. It fractures with extremely sharp edges, making it ideal for ancient weaponry and tools.

Field identification & locations

Easily identified by its smooth, water-worn exterior often with a white chalky cortex, conchoidal fracture showing sharp edges, and a hardness that easily scratches glass. Found worldwide in chalk and limestone formations.