sedimentary

Iron-rich concretion or slag-like rock

Goethite–hematite limonite concretion, possibly iron slag

AI-generated identification · may be incorrect

Dark brown to black, locally metallic or vitreous luster, granular and botryoidal surfaces; likely hardness about 5–6, with no obvious cleavage. Exact density and magnetism would help distinguish natural ironstone from slag.

Identified September 4, 2026More sedimentary →

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Physical properties

Formation & geological history

If natural, it formed by precipitation and cementation of iron oxides/hydroxides in weathered sediments, commonly during the Cenozoic or younger. The smooth glossy areas could alternatively indicate industrial iron slag, a human-processed material.

Uses & applications

Natural specimens are mainly collected for appearance and mineral study; iron ores historically supplied iron. Slag has limited collector value and may be used as aggregate or fill.

Geological facts

The rusty brown color commonly reflects goethite or limonite, while black areas may contain hematite or magnetite. A strong magnet, streak test, and inspection for bubbles or flow textures are useful.

Field identification & locations

Common in iron-rich soils, laterite, stream gravels, and mining districts worldwide; natural concretions often show concentric or irregular growth. A black streak, strong magnetism, or abundant vesicles would refine identification.