sedimentary

Flint or chert

Microcrystalline quartz (SiO₂), commonly with chalcedony

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; dark gray to brown with a waxy to dull luster, fine-grained texture, conchoidal fracture, and no visible cleavage. The pale outer material may be weathered cortex or attached limestone.

Identified August 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or precipitates within limestone, typically during sedimentary diagenesis; specimens may range from Paleozoic to Cenozoic in age. It commonly occurs as nodules, layers, or irregular masses in carbonate rocks.

Uses & applications

Historically used for sharp tools, arrowheads, and fire-starting; today it is mainly collected, studied, or used decoratively. It is not generally a jewelry-grade gemstone unless attractive banding or color is present.

Geological facts

Its conchoidal fracture produces extremely sharp edges, and striking it against steel can create sparks. The image suggests a naturally fractured, possibly worked flint fragment rather than a polished specimen.

Field identification & locations

Identify it by testing for glass-like conchoidal fracture, lack of cleavage, and inability to scratch it with a steel knife; avoid confusing it with obsidian, which is volcanic glass. Common locations include chalk and limestone regions worldwide.