Chert (Flint)

Physical Properties

Hardness: 7 (Mohs scale); Color: Gray, tan, brown with translucent zones; Luster: Waxy to vitreous; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture); SG: 2.65

Formation & Geological History

Formed by the precipitation of silica from water or through the replacement of limestone. Often found as nodules or layers within sedimentary rock sequences like limestone or chalk.

Uses & Applications

Historically used for stone tools (arrowheads, knives) due to sharp edges; used in fire-starting (flint/steel), road construction, and decorative landscaping.

Geological Facts

Known for its conchoidal fracture which produces razor-sharp edges. It has been used by humans for millions of years to create tools and weapons.

Field Identification & Locations

Identify by its hardness (scratches glass), waxy feel, and curved 'shell-like' fracture patterns. Common in gravel beds and limestone cliff exposures.

Identified on: 4/29/2026

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