Limonite (Iron Ore)

Physical Properties

Hardness: 4.0 - 5.5; Color: Yellowish-brown to dark brown; 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 hydration of iron-rich mineral deposits (like pyrite) or as a chemical precipitate in swamps (bog iron).

Uses & Applications

Historically used as a major source of iron ore; currently used as a pigment (brown ochre) and as a low-value collector specimen.

Geological Facts

Limonite is not a single mineral but a mixture of hydrated iron oxide minerals, primarily goethite. It is the substance responsible for the yellowish-brown colors in many soils and weathered rock surfaces.

Field Identification & Locations

Identify in the field by its characteristic 'rust' color and yellow-brown streak when rubbed on a porcelain plate. Often found in weathered zones above iron deposits.

Identified on: 4/13/2026

Mode: Standard