sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: White, grey, or tan interior with a brown weathered cortex; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: White, grey, or tan interior with a brown weathered cortex
Luster: Waxy to vitreous

Identified July 20, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within sedimentary rock layers, often limestone or chalk.

Uses & applications

Used historically for stone tools and starting fires; currently used as construction aggregate, road surfacing, and as a decorative stone in landscaping.

Geological facts

Chert breaks with a conchoidal fracture, creating sharp edges that made it the primary material for arrowheads and spear points throughout human prehistory.

Field identification & locations

Identify in the field by its waxy appearance, extreme hardness (it will scratch glass), and the way it flakes into shell-like curves. Common in riverbeds and limestone outcrops.