mineral

Limonite (Iron Ore)

Limonite (FeO(OH)·nH2O)

Hardness: 4-5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal Structure: Amorphous (often found as pseudomorphs); Specific Gravity: 2.7-4.3.

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

Identified March 21, 2026More mineral →

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Physical properties

Hardness: 4-5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal Structure: Amorphous (often found as pseudomorphs); Specific Gravity: 2.7-4.3.

Formation & geological history

Formed through the oxidation and hydration of iron-rich mineral deposits (like pyrite or magnetite) in weathering environments. It is a secondary mineral found in sedimentary beds and bog iron deposits.

Uses & applications

Historically used as a major iron ore; currently used as a pigment (yellow ochre) in paints, dyes, and as a low-grade coloring agent in concrete and construction.

Geological facts

Limonite is not a true mineral but a mixture of hydrated iron oxide minerals. It was the primary source of 'ochre' used by prehistoric humans for cave paintings and body art.

Field identification & locations

Identify by its distinctive yellowish-brown streak on a porcelain plate and earthy appearance. Commonly found in gossans (weathered tops of ore deposits) and marshy areas. Essential for collectors interested in pseudomorphs.