Limonite/Goethite

Physical Properties

Hardness: 4 to 5.5 (variable); Color: Yellowish-brown to dark brown; Luster: Dull, earthy, or submetallic; Crystal Structure: Amorphous/Orthorhombic; Cleavage: None/Indistinct; Specific Gravity: 2.7 to 4.3.

Formation & Geological History

Formed through the industrial weathering of iron-rich minerals such as magnetite, hematite, or pyrite. It is common in the oxidation zones of ore deposits and as a precipitate in bogs (bog iron).

Uses & Applications

Historically used as a common iron ore and as a natural pigment (brown ochre). It is also valued by collectors for its botryoidal forms and as a marker for metal deposits.

Geological Facts

Limonite is not a true mineral but a mixture of hydrated iron oxide minerals. It has been used by humans as a pigment since prehistoric times, appearing in cave paintings at Lascaux.

Field Identification & Locations

Identify by its characteristic yellowish-brown streak on a porcelain plate and its earthy, rusty appearance. Often found in weathered outcrops or near mine tailings.

Identified on: 5/1/2026

Mode: Standard