mineral

Limonite (with Pyrite)

Limonite (Hydrated Iron Oxide) - FeO(OH)·nH2O

Hardness: 4.0 - 5.5; Color: Yellowish-brown to dark brown; Luster: Dull or earthy; Crystal Structure: Amorphous (often pseudomorphous); Cleavage: None; Specific Gravity: 2.7 - 4.3.

Hardness: 4
Color: Yellowish-brown to dark brown
Luster: Dull or earthy

Identified March 26, 2026More mineral →

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Physical properties

Hardness: 4.0 - 5.5; Color: Yellowish-brown to dark brown; Luster: Dull or earthy; Crystal Structure: Amorphous (often pseudomorphous); Cleavage: None; Specific Gravity: 2.7 - 4.3.

Formation & geological history

Formed by the oxidation and weathering of primary iron-bearing minerals, such as pyrite (fool's gold), or from chemical precipitation in marshy, sedimentary environments (bog iron). It is a secondary mineral found in the oxidation zones of ore deposits.

Uses & applications

Historically used as a major iron ore and as a source of ochre pigment for paints. Today, it is primarily a minor iron ore and a specimen for mineral collectors.

Geological facts

Limonite is not a true mineral but a 'mineraloid' as it lacks a definite crystal structure. It is often found replacing pyrite crystals, resulting in a 'pyrite sun' or a cubic shape that is chemically limonite but structurally pyrite (a pseudomorph).

Field identification & locations

Identify in the field by its characteristic yellowish-brown streak (when rubbed on unglazed porcelain) and earthy appearance. It is commonly found in iron-rich sedimentary beds or near weathered sulfide deposits globally. Collectors look for unique textures or pseudomorphs.

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