mineral

Limonite

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

Hardness: 4.0-5.5; Color: Yellowish-brown to dark brown; Luster: Dull or earthy; Crystal Structure: Amorphous (typically occurs in massive or botryoidal forms); Specific Gravity: 2.7-4.3.

Hardness: 4
Color: Yellowish-brown to dark brown
Luster: Dull or earthy

Identified April 3, 2026More mineral →

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Physical properties

Hardness: 4.0-5.5; Color: Yellowish-brown to dark brown; Luster: Dull or earthy; Crystal Structure: Amorphous (typically occurs in massive or botryoidal forms); Specific Gravity: 2.7-4.3.

Formation & geological history

Formed as a secondary material through the oxidation or weathering of iron-rich minerals like pyrite and magnetite. It is commonly found in the gossans (oxidized caps) above ore deposits and in sedimentary bogs.

Uses & applications

A historic source of iron ore (though less common today than hematite), used as a pigment (Yellow Ochre), and primarily of interest for geological study and mineral collecting.

Geological facts

Limonite is not a singular mineral species but a field term for a mixture of hydrated iron oxides, primarily goethite. It has been used as a pigment by humans for over 30,000 years, appearing in prehistoric cave paintings.

Field identification & locations

Identify in the field by its characteristic yellow-brown streak, dull earthy appearance, and association with weathered iron deposits. It often feels denser than average soil-based rocks but lighter than pure hematite.

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