sedimentary

Chert (often called Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: Grey, tan, or brown, Luster: Waxy to dull, Crystal structure: Hexagonal (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Identified July 3, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: Grey, tan, or brown, Luster: Waxy to dull, Crystal structure: Hexagonal (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of siliceous remains of marine organisms (diatoms, radiolarians) or chemical precipitation from silica-rich groundwater within other sedimentary rocks like limestone.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges; used today as road gravel, in concrete, and historically as the strike for flintlock firearms.

Geological facts

Because of its conchoidal fracture, it can be chipped to an edge only a few molecules thick, making it sharper than a steel scalpel. It is one of the most common materials used in the Stone Age.

Field identification & locations

Identify by its waxy luster, extreme hardness (it will scratch glass), and smooth, curved (conchoidal) breaks. Found worldwide, often as nodules within limestone or chalk beds.