Limonite (Iron Ore)

Physical Properties

Hardness: 4.0–5.5; Color: Yellowish-brown to brownish-orange; Luster: Dull or earthy; Crystal Structure: Amorphous; Cleavage: None; Specific Gravity: 2.7–4.3

Formation & Geological History

Formed as a secondary material through the oxidation and weathering of primary iron-bearing minerals like pyrite and magnetite. It is commonly found in the gossan (oxidized cap) of ore deposits.

Uses & Applications

Primarily used as a low-grade iron ore and as a natural earth pigment (yellow ochre) in paints and dyes.

Geological Facts

Limonite is not a single mineral but a mixture of hydrated iron oxide minerals. It was one of the earliest pigments used by humans, seen in prehistoric cave paintings.

Field Identification & Locations

Identify in the field by its distinct yellow-brown streak when scratched against porcelain and its earthy, ochre-like appearance. Common in wet, weathered environments near iron deposits.

Identified on: 5/11/2026

Mode: Standard