sedimentary

Polished banded chert (likely flint)

Microcrystalline quartz/chalcedony, SiO₂

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; dark gray, olive-brown, and tan bands with a waxy to glossy luster. Very fine-grained, cryptocrystalline, with no visible cleavage; conchoidal fracture is typical.

Identified September 11, 2026More sedimentary →

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Physical properties

Hardness about 6.5–7 Mohs; dark gray, olive-brown, and tan bands with a waxy to glossy luster. Very fine-grained, cryptocrystalline, with no visible cleavage; conchoidal fracture is typical.

Formation & geological history

Formed when silica-rich groundwater replaced or cemented fine sediment, commonly in limestone or chalk, during sedimentary diagenesis. Its exact geological age cannot be determined from the image; chert ranges from Precambrian to modern deposits.

Uses & applications

Used historically for sharp tools and fire-starting, and today for lapidary carvings, polished stones, and decorative pieces. Common specimens generally have modest market value.

Geological facts

The dark banding may reflect changing impurities such as iron, carbon, or manganese during silica deposition. Polishing accentuates the contrasting layers and can make identification resemble jasper or agate.

Field identification & locations

Identify by its opaque fine texture, waxy polish, hardness, and conchoidal edges; it should resist scratching by steel. Common localities include limestone regions worldwide, especially England, Texas, Missouri, Turkey, and parts of India.