Chert (Flint variety)

Physical Properties

Hardness: 7 (Mohs); Color: Dark grey, charcoal, or brown; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline/Microcrystalline quartz; Cleavage: None (displays conchoidal fracture); Specific gravity: 2.65.

Formation & Geological History

Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or by chemical precipitation from silica-rich fluids within other sedimentary rocks like limestone. Often found as nodules within chalk or limestone layers.

Uses & Applications

Historically used for making stone tools (arrowheads, knives) due to sharp edges when fractured. Also used in flintlock firearms and currently in jewelry or as road aggregate.

Geological Facts

Flint was one of the first materials traded by prehistoric humans. When struck against steel, it produces sparks, making it vital for early fire-starting and firearms.

Field Identification & Locations

Identify in the field by its smooth, waxy texture and characteristic shell-like (conchoidal) curved fractures. Very common in regions with limestone outcrops.

Identified on: 4/18/2026

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