sedimentary

Iron-rich flint or chert fragment

Microcrystalline quartz (SiO₂), likely ferruginous chert

AI-generated identification · may be incorrect

Dark brown to black, opaque, with a waxy to dull luster and irregular conchoidal-looking fracture; hardness about 6.5–7 Mohs, no obvious cleavage. The rusty-brown outer material suggests iron-oxide staining or a weathered cortex.

Identified August 10, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica replaces sediment or accumulates from siliceous organisms, later lithifying in sedimentary settings; ferruginous coloring develops during weathering. It may be Cenozoic or older, but age cannot be determined from the photograph.

Uses & applications

Used historically for cutting tools and fire-starting, and today mainly as a collector specimen or lapidary material; attractive pieces can be polished.

Geological facts

The very dark interior and brown weathered rim are characteristic of many flint nodules. It can resemble obsidian, but chert is generally more granular, less glassy, and commonly has a cortex.

Field identification & locations

Common in Central European gravels and sedimentary deposits, including transported material around the Budapest region. Confirm with a hardness test: it should scratch ordinary glass; a streak test is usually absent or white. Exact identification is uncertain without a fresh fracture or tests.