mineral

Limonite-goethite ironstone specimen

Goethite (α-FeO(OH)) with limonite, quartz, and iron oxides

AI-generated identification · may be incorrect

Brown to dark gray, earthy-to-submetallic luster, irregular botryoidal and massive texture; hardness about 4–5.5 Mohs, no obvious cleavage, and relatively high specific gravity (~3.3–4.3).

Identified August 15, 2026More mineral →

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Physical properties

Brown to dark gray, earthy-to-submetallic luster, irregular botryoidal and massive texture; hardness about 4–5.5 Mohs, no obvious cleavage, and relatively high specific gravity (~3.3–4.3).

Formation & geological history

Forms by oxidation and weathering of iron-bearing minerals, commonly producing botryoidal coatings, cavities, or replacement masses in hydrothermal veins and iron-rich soils. It is generally a young surficial alteration product rather than a single age-defined rock.

Uses & applications

Used historically as an iron ore and natural ochre pigment; attractive botryoidal specimens are collected for mineral displays, though it is not normally used as a gemstone.

Geological facts

Limonite is a field term for mixtures of hydrated iron oxides, not a single precisely defined mineral. Goethite commonly forms pseudomorphs and stalactitic or kidney-shaped masses.

Field identification & locations

Identify it by its rusty brown-black color, heavy feel, earthy streak, and association with weathered iron deposits; a yellow-brown to brown streak and lack of fizz in dilute acid support the identification. Common in oxidized ore zones worldwide, including Australia, Brazil, Spain, and the United States.