sedimentary

Chert (Flint)

Microcrystalline / Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness 7 on the Mohs scale; color ranges from grey, white, tan, to brown; waxy to vitreous or dull luster; trigonal crystal system at microcrystalline level; no cleavage, exhibits pronounced conchoidal fracture; specific gravity 2.5–2.8.

Identified September 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through biochemical precipitation of silica from siliceous microorganism skeletons (such as radiolarians or diatoms) in deep-sea or marine carbonate environments, or via diagenetic silica replacement in limestone and chalk beds.

Uses & applications

Historically used in the Stone Age for knapping projectile points, arrowheads, scrapers, and fire-starting (flint and steel). Modernly utilized as construction aggregate, road base material, and occasionally for lapidary tumbling or educational rock specimens.

Geological facts

Due to its hardness and sharp conchoidal fracture edges, chert was one of the earliest and most vital technological materials exploited by prehistoric humans to forge tools and weapons worldwide.

Field identification & locations

Identifiable in the field by its superior hardness (easily scratches glass and steel), lack of reaction to dilute hydrochloric acid, waxy feel, and smooth curved shell-like fractures; commonly found in limestone-rich regions, stream gravels, and chalk formations.