sedimentary

Chert (Black Flint)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Black to charcoal gray; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Black to charcoal gray
Luster: Dull to waxy

Identified July 11, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Black to charcoal gray; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of siliceous remains of marine organisms or chemical precipitation from groundwater. This specimen displays the typical conchoidal fracture of microcrystalline quartz.

Uses & applications

Historically used for making stone tools and starting fires (flint). Currently used in road surfacing and as a decorative stone.

Geological facts

Black chert is often called flint. It was one of the most important materials in human history for crafting arrowheads, knives, and scrappers due to its sharp edges when broken.

Field identification & locations

Identify in the field by its hardness (will scratch glass), sharp edges, and smooth, curved shell-like (conchoidal) fractures. Found in limestone or chalk beds globally.