sedimentary

Chert (specifically Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Tan, brown, and grey with a waxy luster; Crystal Structure: Hexagonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 6
Color: Tan, brown, and grey with a waxy luster

Identified March 19, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Tan, brown, and grey with a waxy luster; Crystal Structure: Hexagonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed as nodules or beds in sedimentary rocks (usually limestone or chalk) via the replacement of carbonates by silica-rich fluids. Often contains microfossils from many geological eras, including the Cretaceous.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) and fire-starting. Currently used as road aggregate, in jewelry as semi-precious gemstones, and in glassmaking.

Geological facts

Because it breaks with a conchoidal fracture, it creates edges sharper than a surgeon's scalpel. It was the premier technology for toolmaking during the Stone Age.

Field identification & locations

Identify in the field by its smooth, waxy surface and the sharp, curved (shell-like) edges where it has broken. Commonly found in riverbeds or within limestone outcrops. Key locations include the UK (Dover), Central USA, and France.