sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7. Color: dark brown to black. Luster: waxy to vitreous. Structure: cryptocrystalline. Known for conchoidal fracture and sharp edges.

Hardness: 6
Color: dark brown to black
Luster: waxy to vitreous

Identified July 19, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7. Color: dark brown to black. Luster: waxy to vitreous. Structure: cryptocrystalline. Known for conchoidal fracture and sharp edges.

Formation & geological history

Formed through the accumulation of siliceous remains of marine organisms or the precipitation of silica from groundwater within limestone or chalk beds. Commonly formed in the Paleozoic to Mesozoic eras.

Uses & applications

Historically used for stone tools and weapons (arrowheads). Today used as aquarium gravel, in road construction, and for fire-starting tools (flint and steel).

Geological facts

Flint is the most common variety of chert. When struck against steel, it produces sparks, which led to its widespread use in early firearms like flintlocks.

Field identification & locations

Identify by its waxy appearance and shell-like (conchoidal) breakage pattern. Found globally in sedimentary basins, often as nodules inside limestone cliffs or as rounded river/beach pebbles.