mineral

Limonite (Ironstone)

Limonite (FeO(OH)·nH2O)

Hardness: 4 to 5.5 on Mohs scale; Color: Dull yellow, brown, to yellowish-brown; Luster: Dull or earthy; Crystal Structure: Amorphous (often found in botryoidal or earthy masses); Specific Gravity: 2.7–4.3.

Hardness: 4 to 5
Color: Dull yellow, brown, to yellowish-brown
Luster: Dull or earthy

Identified June 22, 2026More mineral →

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Physical properties

Formation & geological history

Formed primarily from the chemical weathering of iron-rich minerals such as pyrite, magnetite, and hematite in oxygenated, aqueous environments. It is a secondary mineral often found in oxidation zones of ore deposits.

Uses & applications

Used historically as a source of iron ore; used today as a natural pigment (yellow ochre) in paints, dyes, and coatings. It is also a minor source of ore in some bog-iron deposits.

Geological facts

Limonite is not a true mineral but a mixtures of hydrated iron oxides. It was once widely used by prehistoric humans as 'ochre' for cave paintings and body art due to its staining properties.

Field identification & locations

Identified in the field by its characteristic yellowish-brown streak and earthy appearance. It often forms a 'gossan' or iron hat over sulfide mineral deposits, serving as an indicator for miners searching for more valuable metals underneath.