Limonite (Ironstone)

Physical Properties

Hardness: 4-5.5; Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal Structure: Amorphous or cryptocrystalline; Specific Gravity: 2.7-4.3

Formation & Geological History

Formed by the oxidation and weathering of iron-rich ores like magnetite and hematite. It commonly forms in secondary enrichment zones, bog deposits, or as a coating on other minerals.

Uses & Applications

Historically used as a major iron ore and as a source of yellow ochre pigment. Currently used for soil conditioning and by mineral collectors.

Geological Facts

Limonite is not a stand-alone mineral species but a mixture of hydrated iron oxide minerals, primarily goethite. It was the preferred source of pigments for early cave paintings.

Field Identification & Locations

Identify by its brownish-yellow streak and lack of magnetism (unlike magnetite). Found globally, particularly in weathering environments and sedimentary basins.

Identified on: 4/30/2026

Mode: Standard