Mineral

Limonite (Iron Ore)

Limonite (Hydrated Iron Oxide, FeO(OH)·nH2O)

Hardness: 4-5.5 (Mohs scale); Color: Yellow-brown to dark brown; Luster: Dull, earthy; Crystal structure: Amorphous; Cleavage: None; Specific gravity: 2.7-4.3.

Hardness: 4-5
Color: Yellow-brown to dark brown
Luster: Dull, earthy

Identified March 1, 2026More mineral →

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Physical properties

Hardness: 4-5.5 (Mohs scale); Color: Yellow-brown to dark brown; Luster: Dull, earthy; Crystal structure: Amorphous; Cleavage: None; Specific gravity: 2.7-4.3.

Formation & geological history

Formed as a secondary material through the oxidation and weathering of primary iron-bearing minerals like pyrite, magnetite, and hematite. It is commonly found in the oxidized zones of ore deposits and as bog iron.

Uses & applications

Historically used as a major iron ore; today mostly used as a mineral pigment (yellow ochre) in paints, ceramics, and as a soil conditioner.

Geological facts

Limonite is not a true mineral but a mineraloid composed of various iron oxides. It was a primary source of iron for many ancient civilizations during the Iron Age.

Field identification & locations

Identify in the field by its characteristic yellow-brown streak (powder) when scraped against a hard surface. It is commonly found in sedimentary environments, swamps, and as gossan (iron caps) over ore veins.

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