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
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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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Gypsum (variety Selenite or Alabaster)
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Mineral/Rock
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