sedimentary

Flint (or Chert)

Microcrystalline quartz (SiO2)

Hardness: 7 on the Mohs scale. Color: Varies from dark grey, blue, black, to light brown and white, often with a chalky cortex exterior. Luster: Vitreous to waxy or dull. Crystal structure: Cryptocrystalline / microfibrous quartz (chalcedony). Cleavage: None (exhibits prominent conchoidal fracture).…

Hardness: 7 on the Mohs scale
Luster: Vitreous to waxy or dull

Identified July 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed diagenetically through the replacement of calcium carbonate in limestone or chalk by silica-rich solutions, or through the accumulation of siliceous skeletal remains of marine organisms like radiolarians and diatoms, typically dating from the Cretaceous period.

Uses & applications

Historically used extensively for making stone tools, arrowheads, and blades due to its sharp conchoidal fracture; later used for fire-starting with steel and in flintlock firearms; today primarily collected as a geological specimen.

Geological facts

Flint and chert are essentially the same mineral material, though the term 'flint' is traditionally reserved for dark varieties found in chalk deposits. Because of its extreme durability and sharp edges when broken, it was one of the most valuable materials for early human technology.

Field identification & locations

Easily identified by its characteristic conchoidal fracture (smooth, curved shell-like break surfaces), waxy luster, and high hardness capable of scratching glass. Commonly found weathering out of limestone or chalk formations worldwide.