sedimentary

Chert (Flint nodule)

Microcrystalline / Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on the Mohs scale; Color: Gray, brownish-gray with a lighter chalky weathering rind (cortex); Luster: Waxy to vitreous or dull; Cleavage: None (distinct conchoidal fracture); Specific gravity: ~2.65

Hardness: 7 on the Mohs scale
Luster: Waxy to vitreous or dull

Identified November 15, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of biogenic silica (such as radiolarian or sponge spicule remains) or chemical precipitation within sedimentary rocks like limestone or chalk during diagenesis.

Uses & applications

Historically used for knapping stone tools, arrowheads, and spark generation in flintlock firearms. Currently used as an abrasive, decorative stone, construction aggregate, and by hobbyist flintknappers.

Geological facts

Flint was crucial to early human technological advancement due to its predictable conchoidal fracture which creates razor-sharp edges. When struck against steel or iron pyrite, it easily generates sparks hot enough to ignite tinder.

Field identification & locations

Easily recognized in the field by its extreme hardness (scratches glass/steel easily), curved/shell-like conchoidal fracture, and often a pale outer cortex when found in marine limestone or chalk formations. Widely abundant worldwide in marine sedimentary basins.