Limonite: The Hydrated Iron Ore
Limonite is an important iron ore mineral composed mainly of hydrated iron oxides such as FeO(OH)·nH₂O. Unlike other iron ores like hematite or magnetite, limonite is not a distinct mineral but rather a mixture of various iron oxide minerals with water content.
Key Characteristics of Limonite
✅ Color: Yellow, brown, or ochre shades (rust-like appearance).
✅ Streak: Yellow-brown.
✅ Hardness: 4 – 5.5 on Mohs scale (moderately hard).
✅ Luster: Dull to earthy.
✅ Specific Gravity: 2.7 – 4.3 (variable due to its mixed nature).
✅ Structure: Often appears as amorphous masses, botryoidal (grape-like), or earthy coatings.
Formation of Limonite
Limonite forms mainly through the weathering and oxidation of iron-rich minerals such as:
🔹 Pyrite (FeS₂) → When exposed to oxygen and water, pyrite breaks down into limonite.
🔹 Hematite & Magnetite → Over time, these minerals may hydrate and transform into limonite.
It is commonly found in bogs, swamps, and iron-rich soils as a result of oxidation processes.
Occurrence and Distribution
Limonite is widely found in tropical and subtropical regions, where intense weathering occurs. Major deposits exist in:
- India – Odisha, Jharkhand, and Chhattisgarh.
- USA – In iron-rich regions like Pennsylvania.