sedimentary

Chert (Flint)

Chert (Microcrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs; Color: White, gray, tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 Mohs
Color: White, gray, tan
Luster: Waxy to dull

Identified July 2, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: White, gray, tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed primarily through the chemical precipitation of silica-rich fluids or the accumulation of siliceous remains (like diatoms or radiolaria) in sedimentary basins, often occurring as nodules in limestone or chalk.

Uses & applications

Historically used for stone tools (knapping) and fire-starting; currently used as a decorative stone, in road construction, and for jewelry like cabochons.

Geological facts

Flint is a variety of chert that was essential to prehistoric humans for making arrowheads and spear points due to its sharp, conchoidal fracture edges.

Field identification & locations

Identify by its extreme hardness (scratches glass), waxy luster, and smooth, curved fracture surfaces. Commonly found in limestone outcrops or as river pebbles.