sedimentary

Blue-gray flint or chert fragment

Microcrystalline quartz (SiO₂), likely flint/chert

AI-generated identification · may be incorrect

Hardness about 7 Mohs; blue-gray to dark gray, glassy to waxy luster, very fine-grained cryptocrystalline structure, no visible cleavage, and conchoidal fracture with sharp edges. The small size and lighting make exact identification uncertain.

Identified August 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich fluids replace or cement sediment, commonly as nodules or beds in limestone and chalk; many specimens are Paleozoic to Cenozoic, depending on locality. Its shape may reflect natural breakage or human knapping.

Uses & applications

Used historically for tools, arrowheads, fire-starting, and road aggregate; attractive polished varieties are collected, but ordinary fragments have little commercial value.

Geological facts

Flint is a dense variety of chert and can produce exceptionally sharp edges. A blue color may result from impurities or lighting and is not diagnostic by itself.

Field identification & locations

Look for extreme hardness, opacity or translucency at thin edges, waxy/glassy luster, and curved fracture surfaces; it should scratch glass. Common in limestone regions worldwide, including England, France, the Great Lakes, and Texas.