mineral

Limonite (Iron Ore)

Limonite (FeO(OH)·nH2O)

Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to dark brown or black; Luster: Dull, earthy, or submetallic; Crystal structure: Amorphous; Cleavage: None; Specific Gravity: 2.7-4.3.

Hardness: 4-5
Color: Yellowish-brown to dark brown or black
Luster: Dull, earthy, or submetallic

Identified April 7, 2026More mineral →

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Physical properties

Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to dark brown or black; Luster: Dull, earthy, or submetallic; Crystal structure: Amorphous; Cleavage: None; Specific Gravity: 2.7-4.3.

Formation & geological history

Formed as a secondary mineral through the oxidation and hydration of iron-rich minerals (like pyrite, magnetite, or hematite) in weathered zones of ore deposits. It can also form in bog environments.

Uses & applications

A major source of iron ore; used as an iron-oxide pigment (yellow ochre) in paints, plastics, and ceramics; historically used as a coloring agent for cosmetics.

Geological facts

Limonite isn't a single mineral but a mixture of hydrated iron oxide minerals, primarily goethite. It is one of the most common iron minerals and gives red, orange, and yellow hues to soil and sandstone.

Field identification & locations

Identify in the field by its characteristic yellowish-brown streak on a porcelain plate and its earthy, non-metallic luster. Commonly found in gossans (weathered rock caps) over sulfide deposits and in sedimentary bog iron deposits.