sedimentary

Chert (Flint)

Microcrystalline silica (SiO2)

Hardness: 7 on Mohs scale; Color: brown, tan, gray; Luster: waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: brown, tan, gray
Luster: waxy to dull

Identified June 12, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: brown, tan, gray; Luster: waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed by the precipitation of silica from groundwater or the accumulation of siliceous skeletal remains of marine organisms. Common in the sedimentary basins near Saratov (51.5N, 45.9E) within Cretaceous limestone and chalk deposits.

Uses & applications

Historically used for stone tools and starting fires (flint); currently used as a decorative stone, in construction aggregate, and as a specimen for collectors.

Geological facts

Flint is a variety of chert that occurs primarily in chalk or marly limestone. It has been used by humans for millions of years to create sharp-edged tools due to its predictable conchoidal fracturing.

Field identification & locations

Identify by its hardness (scratches glass), waxy texture, and shell-like (conchoidal) fracture pattern. It is very common in the Volga region of Russia.