sedimentary

Banded chert or flint

Microcrystalline quartz (SiO₂), commonly called chert/flint

AI-generated identification · may be incorrect

Typically very fine-grained, dark gray to black, with waxy-to-dull luster and curved conchoidal fracture; Mohs hardness about 6.5–7, no cleavage, specific gravity roughly 2.6. The visible parallel bands may reflect layered silica-rich sediment or replacement textures.

Identified September 13, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica from microscopic organisms or groundwater precipitates and replaces carbonate or other sediments, commonly during the Paleozoic–Mesozoic and younger periods. Exact age and locality cannot be determined from the image alone.

Uses & applications

Used historically for stone tools, arrowheads, and fire-starting; today it is mainly a lapidary, teaching, and collecting material, with limited aggregate use.

Geological facts

Its exceptionally fine grain permits sharp edges and conchoidal fracture. Dark color often results from organic matter, iron, or manganese impurities.

Field identification & locations

Look for hardness sufficient to scratch glass, lack of visible individual crystals, and smooth shell-like fracture; streak is usually white to gray. Common in sedimentary formations worldwide, including chalk, limestone, and nodular beds.