sedimentary

Chert (Flint)

Chert (Silica, SiO2)

Hardness: 7 (Mohs scale), Color: tan, grey, brown; Luster: waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline (trigonal); Cleavage: none (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale), Color: tan, grey, brown
Color: tan, grey, brown
Luster: waxy to dull

Identified April 5, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: tan, grey, brown; Luster: waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline (trigonal); Cleavage: none (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed from the accumulation of microscopic silica shells (radiolarians or diatoms) or by chemical precipitation in limestone/chalk beds. Found in sedimentary layers globally, often dating from the Precambrian to Cenozoic eras.

Uses & applications

Historically used for stone tools (arrowheads, knives) due to its sharp edges; used in construction aggregates, road metal, and as a component in early flintlock firearms.

Geological facts

Chert is so hard that it can scratch steel and produce sparks when struck against iron, which led to its extensive use in fire-starting kits and flintlock rifles.

Field identification & locations

Identify in the field by its smooth, waxy surface and distinct conchoidal (shell-like) fracture patterns. It is extremely common in areas with limestone or chalk outcroppings.