mineral

Limonite (Ironstone)

Limonite (Hydrated iron(III) oxide-hydroxide, FeO(OH)·nH2O)

Hardness: 4-5.5; Color: Yellowish-brown to dark brown; Luster: Dull/Earthy; Crystal Structure: Amorphous (often pseudomorphic after other minerals); Streak: Yellow-brown.

Hardness: 4-5
Color: Yellowish-brown to dark brown
Luster: Dull/Earthy

Identified April 20, 2026More mineral →

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Physical properties

Hardness: 4-5.5; Color: Yellowish-brown to dark brown; Luster: Dull/Earthy; Crystal Structure: Amorphous (often pseudomorphic after other minerals); Streak: Yellow-brown.

Formation & geological history

Formed as a secondary mineral through the oxidation and weathering of iron-rich minerals such as pyrite, magnetite, and siderite. Commonly found in gossans (iron hats) above ore deposits and in bog iron deposits.

Uses & applications

Historically used as a minor ore of iron; primarily used today as a natural earth pigment (yellow ochre) in paints and dyes. Significant in soil science for indicating oxidation states.

Geological facts

Limonite is not a true mineral but a mineraloid composed of varying mixtures of goethite and other iron oxides. It was once a major source of iron for early civilizations and bog iron production.

Field identification & locations

Identify by its distinctive yellow-brown streak, earthy appearance, and lack of cleavage. Found globally in weathered zones/areas with high iron content. Tips for collectors: check for pseudomorphs of pyrite (iron pyrites) which are more valuable.

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