sedimentary

Chert / Flint

Silicon dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Black, grey, or dark brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

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

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Black, grey, or dark brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed by the accumulation of siliceous remains of organisms (like diatoms or radiolarians) or chemical precipitation in sedimentary environments. May occur as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools (arrowheads, knives) and striking fire. Currently used as a construction aggregate, in road surfacing, and as a pocket stone for collectors.

Geological facts

Flint is a variety of chert. When struck against steel, it produces sparks due to the friction oxidizing iron particles. It was the primary material for the Neolithic 'Stone Age' technology.

Field identification & locations

Identify by its 'glassy' conchoidal fracture which creates sharp edges. It is harder than steel and will scratch a glass plate. Found globally in sedimentary rock outcrops.