sedimentary

Chert / Flint

Silicon dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: tan, brown, reddish; Luster: waxy to vitreous; Structure: cryptocrystalline; Cleavage: none, exhibits conchoidal fracture

Hardness: 7 on Mohs scale
Color: tan, brown, reddish
Luster: waxy to vitreous

Identified July 15, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: tan, brown, reddish; Luster: waxy to vitreous; Structure: cryptocrystalline; Cleavage: none, exhibits conchoidal fracture

Formation & geological history

Formed by the accumulation of siliceous remains of organisms (like diatoms) or by chemical precipitation of silica in marine environments, often within limestone or chalk beds.

Uses & applications

Historically used for stone tools and starting fires; currently used for landscaping, road construction, and as a collector's item due to its sharp fracturing properties.

Geological facts

Flint is a specific variety of chert. Because it breaks into very sharp edges, it was the primary material for prehistoric arrowheads and knives.

Field identification & locations

Identify by its waxy luster, lack of visible crystals, and sharp, shell-like (conchoidal) breakage patterns. The round specimen in the background is likely a chert nodule or concretion.