mineral
Limonite (Iron Ore)
Limonite (mixed iron hydroxides, primarily FeO(OH)·nH2O)
Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to dark brown or black; Luster: Dull, earthy; Crystal System: Amorphous/microcrystalline; Streak: Yellow-brown; Specific Gravity: 2.7-4.3
- Hardness
- 4-5
- Color
- Yellowish-brown to dark brown or black
- Luster
- Dull, earthy
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Physical properties
Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to dark brown or black; Luster: Dull, earthy; Crystal System: Amorphous/microcrystalline; Streak: Yellow-brown; Specific Gravity: 2.7-4.3
Formation & geological history
Formed as a secondary mineral through the weathering and oxidation of other iron-bearing minerals (like pyrite, magnetite, or siderite). Commonly found in the oxidation zones of ore deposits and as bog iron.
Uses & applications
Historically used as a major source of iron ore and as a natural pigment (yellow ochre) for paints and dyes. Small specimens are collected for geological study.
Geological facts
Limonite is not a true mineral but a mixture of hydrated iron oxide minerals. It was the primary source of iron for many early human civilizations and is responsible for the distinct yellow/rusty color of many soils.
Field identification & locations
Identify by its earthy appearance and characteristic yellow-brown streak (scrape it against unglazed porcelain). It is commonly found in sedimentary environments and near weathered iron deposits.
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