mineral

Limonite (Iron Ore)

Limonite (FeO(OH)·nH2O)

Hardness: 4-5.5 (Mohs), Color: Yellowish-brown to dark brown/black, Luster: Dull or earthy, Crystal Structure: Amorphous (often pseudomorphous), Streak: Yellow-brown.

Hardness: 4-5
Streak: Yellow-brown

Identified July 7, 2026More mineral →

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Physical properties

Hardness: 4-5.5 (Mohs), Color: Yellowish-brown to dark brown/black, Luster: Dull or earthy, Crystal Structure: Amorphous (often pseudomorphous), Streak: Yellow-brown.

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 metamorphic layers.

Uses & applications

Historically used as a primary iron ore and as a source of ochre pigment for paints and dyes. Currently used in soil conditioning and as a minor source of iron.

Geological facts

Limonite is not a single mineral but a mixture of hydrated iron oxide minerals. It was the source of 'wild iron' used by early blacksmiths and is the pigment that gives rust its color.

Field identification & locations

Identified by its distinctive yellowish-brown streak on a porcelain plate and its earthy, rusty appearance. Commonly found in boggy areas or weathered rock outcrops.