sedimentary

Chert (often called Flint)

Chert (Silicon Dioxide, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Gray, tan, or black; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline (microscopic quartz crystals); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Gray, tan, or black
Luster: Waxy to dull

Identified May 10, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich organic remains such as radiolaria or diatoms on the ocean floor, or through chemical precipitation from groundwater within limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) and as fire-starters. Industrially used as an abrasive and in gemstone tumbling.

Geological facts

Because it breaks with a conchoidal fracture, it creates edges thinner and sharper than a surgical steel scalpel. It has been used by humans for over 2 million years.

Field identification & locations

Identify by its waxy texture, extreme hardness (it will scratch glass), and the shell-like (conchoidal) curves where it is broken. Commonly found in limestone outcrops or as river pebbles.