mineral

Limonite (Iron Ore)

FeO(OH)·nH2O (Hydrated Iron Oxide)

Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal Structure: Amorphous (non-crystalline); Cleavage: None; Specific Gravity: 2.7-4.3

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

Identified April 7, 2026More mineral →

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Physical properties

Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal Structure: Amorphous (non-crystalline); Cleavage: None; Specific Gravity: 2.7-4.3

Formation & geological history

Formed as a secondary mineral through the weathering and oxidation of iron-rich minerals such as pyrite, magnetite, and siderite. Often found in bogs, lake beds, or as a gossip (weathered cap) over sulfide deposits.

Uses & applications

Major historical source of iron ore; used as a pigment (yellow ochre) in paints, dyes, and cosmetics; used in fertilizers and as a source of iron in early metallurgy.

Geological facts

Limonite was the primary source of 'bog iron' used during the Industrial Revolution. It is actually a mixture of multiple iron minerals rather than a single distinct mineral species.

Field identification & locations

Identify by its distinctive yellowish-brown streak on a porcelain plate and earthy appearance. It is found globally in sedimentary basins and weathered rock zones. Tips for collectors: check for relatively high weight compared to size (density).

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