mineral

Limonite (Ironstone)

Hydrous ferric oxides (FeO(OH)·nH2O)

Hardness: 4-5.5; Color: Yellowish-brown to dark brown; Luster: Dull or earthy; Crystal Structure: Amorphous; Streak: Yellow-brown; Specific Gravity: 2.7-4.3

Hardness: 4-5
Color: Yellowish-brown to dark brown
Luster: Dull or earthy

Identified May 7, 2026More mineral →

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Physical properties

Hardness: 4-5.5; Color: Yellowish-brown to dark brown; Luster: Dull or earthy; Crystal Structure: Amorphous; Streak: Yellow-brown; Specific Gravity: 2.7-4.3

Formation & geological history

Formed as a secondary mineral through the oxidation and hydration of iron-rich primary minerals such as pyrite or magnetite; often found in bog deposits or weathered outcrops.

Uses & applications

Historically used as a minor iron ore and as a source of ochre pigment (yellow/brown) for paints and cosmetics.

Geological facts

Limonite is not a true mineral in the strictest sense but a mixture of various hydrous iron oxides, primarily goethite. It was the primary ingredient for brown cave paintings in prehistoric times.

Field identification & locations

Identify in the field by its distinct mustard-yellow or rusty-brown streak when scratched on porcelain. Commonly found in gossans (weathered tops of ore deposits).

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