Rock Identifier
Limonite (Iron Stone/Goethite) (Limonite (mixture of hydrated iron oxides, primarily Goethite: α-FeO(OH))) — mineral
mineral

Limonite (Iron Stone/Goethite)

Limonite (mixture of hydrated iron oxides, primarily Goethite: α-FeO(OH))

Hardness: 4.0-5.5 (Mohs scale); Color: Dark brown to yellow-brown; Luster: Dull, earthy, or sub-metallic; Crystal Structure: Amorphous or microcrystalline; Specific Gravity: 2.7 to 4.3.

Hardness
4
Color
Dark brown to yellow-brown
Luster
Dull, earthy, or sub-metallic
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Physical properties

Hardness: 4.0-5.5 (Mohs scale); Color: Dark brown to yellow-brown; Luster: Dull, earthy, or sub-metallic; Crystal Structure: Amorphous or microcrystalline; Specific Gravity: 2.7 to 4.3.

Formation & geological history

Formed as a secondary mineral through the weathering of iron-rich ores such as magnetite, hematite, or pyrite. It is common in sedimentary environments and soil horizons as bog iron or ironstone.

Uses & applications

Historically used as a minor iron ore; currently used as a natural pigment (brown ochre) in paints, and occasionally for lapidary work or as a collection specimen.

Geological facts

Limonite is not a true mineral but a mineraloid. It was the primary source of 'ochre' used by early humans for cave paintings. Many 'meteor-wrongs' or fake meteorites found in fields are actually limonite concretions.

Field identification & locations

Identify in the field by its distinct yellow-brown streak (scratching it against unglazed porcelain), its relative heaviness compared to non-metallic rocks, and its lack of magnetism (unlike magnetite). Commonly found in wetlands, iron-rich stream beds, and oxidized zones of ore deposits.

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