Limonite (Iron Ore)

Physical Properties

Hardness: 4.0-5.5; Color: Yellow-brown to charcoal; Luster: Dull, earthy; Crystal Structure: Amorphous; Cleavage: None; Specific Gravity: 2.7-4.3

Formation & Geological History

Formed as a secondary mineral produced from the chemical weathering of iron-rich primary minerals such as hematite, magnetite, or pyrite. It is common in soil and gossans (oxidized caps above metallic deposits).

Uses & Applications

A major source of iron ore globally; historically used as a natural pigment (yellow ochre) for paints and cosmetics. Also used in cement production.

Geological Facts

Limonite is not a single mineral but a mixture of hydrated iron oxide minerals. It was the source of the yellow ochre used by ancient humans in cave paintings and is also responsible for the color of 'yellow soils'.

Field Identification & Locations

Identify in the field by its characteristic yellowish-brown streak on a porcelain plate and its earthy, non-metallic appearance. Commonly found in marshy areas (bog iron) or as 'rust' on weathered outcrops.

Identified on: 4/28/2026

Mode: Standard