mineral

Limonite/Goethite Nodule

Iron Oxyhydroxide (primarily FeO(OH)·nH2O)

Hardness: 4-5.5 (variable); Color: Dull brownish-yellow to dark brown; Luster: Earthy to dull; Crystal structure: Amorphous or cryptocrystalline; Cleavage: None; Specific gravity: 2.7-4.3.

Hardness: 4-5
Color: Dull brownish-yellow to dark brown
Luster: Earthy to dull

Identified April 12, 2026More mineral →

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Physical properties

Hardness: 4-5.5 (variable); Color: Dull brownish-yellow to dark brown; Luster: Earthy to dull; Crystal structure: Amorphous or cryptocrystalline; Cleavage: None; Specific gravity: 2.7-4.3.

Formation & geological history

Formed by the oxidation and hydration of existing iron-rich minerals (like pyrite or magnetite) in weathered environments. It is a secondary mineral commonly found in soil and oxidation zones of ore deposits.

Uses & applications

Historically used as a low-grade iron ore and as a source of ochre pigments for paints and dyes. In modern times, it is mostly a geological indicator for prospectors.

Geological facts

Limonite was one of the earliest pigments used by humans, seen in prehistoric cave paintings. It often forms pseudomorphs, taking the crystal shape of the mineral it replaced.

Field identification & locations

Identify in the field by its characteristic yellowish-brown streak on a porcelain plate and its dull, rocky appearance. Frequently found in stream beds or weathered outcrops.

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