sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, white, gray, or brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, white, gray, or brown
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, white, gray, or brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed via the accumulation of siliceous oozes from microscopic organisms like diatoms or radiolarians, or through chemical precipitation of silica in groundwater within carbonate rocks. Found in strata ranging from Precambrian to recent.

Uses & applications

Historically used for stone tools and starting fires (flint); currently used in road construction, as jewelry (jasper varieties), and as a gemstone when colorful.

Geological facts

Because it breaks with a conchoidal fracture like glass, it creates extremely sharp edges, which is why it was the primary material for arrowheads and knives for thousands of years.

Field identification & locations

Identify by its extreme hardness (scratches glass), waxy feel, and smooth curved (conchoidal) fractures. Often found as nodules within limestone or chalk beds.