Limonite (Iron Ore)

Physical Properties

Hardness: 4.0-5.5 (Mohs scale); Color: Yellowish-brown to ochre; Luster: Dull, earthy; Crystal Structure: Amorphous; Cleavage: None; Specific Gravity: 2.7-4.3

Formation & Geological History

Formed as a secondary material through the oxidation and precipitation of other iron-rich minerals (like pyrite or magnetite) in weathered zones and sedimentary bogs.

Uses & Applications

Major historical source of iron ore; used as a natural earth pigment (yellow ochre) in paints, dyes, and coatings.

Geological Facts

Limonite was used by cave painters over 30,000 years ago to create yellow and brown colors. It is often found as 'iron hat' or gossan cap over metal ore deposits.

Field Identification & Locations

Identify by its characteristic yellowish-brown streak on a porcelain plate and its earthy, yellowish weathered appearance on rocks. Common in wet soils and near oxidizing sulfide veins.

Identified on: 5/8/2026

Mode: Standard