mineral

Limonite (Iron Stone/Iron Ore)

FeO(OH)·nH2O (Hydrous ferric oxide)

Hardness: 4.0-5.5 (Mohs scale); Color: Yellowish-brown to dark brown; Luster: Dull or earthy; Crystal structure: Amorphous; Cleavage: None; Specific gravity: 2.7-4.3

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

Identified March 1, 2026More mineral →

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Physical properties

Hardness: 4.0-5.5 (Mohs scale); Color: Yellowish-brown to dark brown; Luster: Dull or earthy; Crystal structure: Amorphous; Cleavage: None; Specific gravity: 2.7-4.3

Formation & geological history

Formed as a secondary material through the oxidation and hydration of iron-rich mineral ores (like pyrite or magnetite) in weathering zones. It can occur in sedimentary layers or as gossans over metal deposits.

Uses & applications

Historically used as an iron ore; currently used as a natural pigment (yellow ochre) in paints, and occasionally as a low-cost building material or for minor geological teaching kits.

Geological facts

Limonite is not a true mineral species but a mixture of similar hydrated iron oxide minerals, predominantly goethite. It's the primary component of 'iron hat' or gossan, which prospectors use to find gold and copper deposits.

Field identification & locations

Identify in the field by its distinct mustard-yellow to rust-brown streak (test by scratching on unglazed porcelain) and its earthy, dull appearance. Common in wet soils and boggy environments.

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