mineral
Limonite (Iron Ore/Bog Iron)
Hydrated iron(III) oxide-hydroxide (FeO(OH)nH2O)
Hardness: 4-5.5; Color: Yellow-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous (often pseudomorphous); Streak: Yellow-brown.
- Hardness
- 4-5
- Color
- Yellow-brown to dark brown
- Luster
- Dull to earthy
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Physical properties
Hardness: 4-5.5; Color: Yellow-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous (often pseudomorphous); Streak: Yellow-brown.
Formation & geological history
Formed as a secondary mineral through the oxidation and hydration of iron-rich primary minerals such as pyrite, magnetite, and hematite in weathering zones.
Uses & applications
Primarily used as a low-grade iron ore and as a pigment (brown and yellow ochre). Historically used as a material for early iron smelting.
Geological facts
Limonite is not a true mineral species but a mixture of hydrated iron oxide minerals. It was the primary source of 'ochre' used in prehistoric cave paintings.
Field identification & locations
Identify by its yellowish-brown streak on a porcelain plate and its earthy, rusty appearance. Often found in boggy areas or as gossan caps over ore deposits.
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