sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, white, brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Gray, tan, white, brown
Luster: Waxy to dull

Identified June 6, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, tan, white, brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed through the accumulation of siliceous remains of marine organisms or via chemical precipitation in sedimentary basins. Often found as nodules within limestone or chalk beds.

Uses & applications

Historically used for stone tools and starting fires; modernly used in road construction, as abrasive materials, and occasionally as semi-precious gemstones in jewelry.

Geological facts

Chert has been used by humans for over two million years to create sharp-edged tools like arrowheads and knives due to its predictable conchoidal fracturing.

Field identification & locations

Identify by its extreme hardness (scratches glass), waxy feel, and smooth, shell-like (conchoidal) breaks. Commonly found along riverbeds, beaches, and limestone outcrops.