Limonite (Iron Ore)

Physical Properties

Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to dark brown/black; Luster: Dull to sub-metallic; Crystal Structure: Amorphous/Massive; Cleavage: None; Specific Gravity: 2.7-4.3

Formation & Geological History

Formed through the chemical weathering of iron-rich minerals (such as pyrite or magnetite) or as a precipitate in bogs, lakes, and marine environments. Often found as a secondary mineral in oxidation zones.

Uses & Applications

Primary source of iron ore; historically used as a yellow-ochre pigment in paints and dyes. Currently used in soil conditioners and for industrial iron production.

Geological Facts

Limonite is not a true mineral but a mixture of hydrated iron oxides. It was a major source of 'bog iron' used during the early industrial revolution and by the Vikings for tool making.

Field Identification & Locations

Identify by its characteristic yellowish-brown streak (when rubbed against porcelain) and its rusty, earthy appearance. Common in weathered rock outcrops and sedimentary basins.

Identified on: 4/27/2026

Mode: Standard