mineral

Limonite (Iron Ore)

Limonite (FeO(OH)·nH2O)

Hardness: 4.0-5.5; Color: Yellowish-brown to dark brown/black; Luster: Dull, earthy, or sub-metallic; Crystal Structure: Amorphous (often pseudomorphous); Cleavage: None; Specific Gravity: 2.7-4.3

Hardness: 4
Color: Yellowish-brown to dark brown/black
Luster: Dull, earthy, or sub-metallic

Identified June 27, 2026More mineral →

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Physical properties

Hardness: 4.0-5.5; Color: Yellowish-brown to dark brown/black; Luster: Dull, earthy, or sub-metallic; Crystal Structure: Amorphous (often pseudomorphous); Cleavage: None; Specific Gravity: 2.7-4.3

Formation & geological history

Formed as a secondary material through the oxidation and weathering of iron-rich minerals such as pyrite, magnetite, and hematite in sedimentary or boggy environments.

Uses & applications

Historically used as a major source of iron ore and as a natural earth pigment (yellow ochre) in paints and dyes.

Geological facts

Limonite is not a true mineral but a mixture of hydrated iron oxide minerals. It was used by ancient civilizations for cave paintings and is still a coloring agent in bricks and concrete.

Field identification & locations

Identify in the field by its yellowish-brown streak, rusty appearance, and lack of magnetism (unlike magnetite). Commonly found in gossans and sedimentary iron deposits.