sedimentary

Chert / Flint

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: White, grey, black (often variegated); Luster: Waxy to dull; Crystal structure: Microcrystalline (cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: White, grey, black (often variegated)
Luster: Waxy to dull

Identified March 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the precipitation of silica in sedimentary environments, often replacing organic material or occurring as nodules in limestone/chalk beds. It can range from very recent to billions of years old (Precambrian).

Uses & applications

Historically used for stone tools and weapons (arrowheads). Modernly used as a flux in ceramics, for road base material, and occasionally in lapidary work or as fire-starting flint.

Geological facts

Because it breaks with a conchoidal (shell-like) fracture, it produces edges sharper than a surgeon's scalpel. It was the primary technological material for most of human history during the Stone Age.

Field identification & locations

Identify in the field by its sharp, curved edges when broken and its ability to scratch glass. It is commonly found in chalk or limestone deposits, riverbeds, and glacial till. Collectors look for unique colors or 'bullseye' patterns.