sedimentary

Weathered iron-rich concretion or ironstone cobble

Goethite–hematite–limonite-rich ironstone; exact identification requires testing

AI-generated identification · may be incorrect

Hardness typically 5–6.5 Mohs; dark brown, rusty red, gray-black; earthy to submetallic luster; dense, fine-grained, and commonly porous or pitted. May be weakly magnetic if magnetite is present; no visible cleavage or crystals.

Identified September 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Likely formed as a sedimentary ironstone concretion or heavily weathered iron-rich rock, with oxidation producing limonite/goethite and hematite. Such material commonly forms in soils, river gravels, and iron-bearing sedimentary deposits; age cannot be determined from the image.

Uses & applications

Used as iron ore when sufficiently concentrated, pigment, aggregate, or a curiosity specimen; generally not suitable for jewelry unless polished. Common pieces have modest collector value.

Geological facts

The rounded shape and surface cavities suggest prolonged transport or weathering, while reddish-brown coloration indicates oxidized iron. A streak test, magnet test, density measurement, and fresh-surface examination would distinguish ironstone from slag or meteorite material.

Field identification & locations

Common in iron-rich soils and gravels worldwide, especially around banded iron formations and lateritic regions. Test streak on unglazed porcelain: red-brown suggests hematite, yellow-brown suggests goethite/limonite; slag may show glassy texture and bubbles.