Limonite

Chemical Composition and Properties

– General Formula: FeO(OH) · nH₂O (where “n” represents the varying amount of water in its structure)

– Primary Components: Iron(III) oxide-hydroxide with varying levels of hydration

– Iron Content: Typically around 50% to 66% iron by weight

– Colour: Ranges from yellow to brown to black, depending on impurities and weathering

– Crystal System: Amorphous to earthy or cryptocrystalline (not typically in well-defined crystals)

– Hardness: 4 – 5.5 on the Mohs scale

– Specific Gravity: 2.7 – 4.3

Chemical Information

– CAS Number: 1317-63-1 (for hydrated iron oxide, commonly used to refer to limonite as well)

– Chemical Composition: A mix of iron oxides, hydroxides, and water molecules in variable amounts, commonly represented by FeO(OH) · nH₂O.

– Molecular Weight: Variable, due to the fluctuating hydration state

– HS Code: 2601.20.00.00 (for iron ores and concentrates, other than roasted iron pyrites)

Formation and Occurrence
Limonite is often formed in the oxidation zones of iron-rich deposits. It can also occur as a secondary mineral from the weathering of iron-bearing rocks and minerals such as pyrite, magnetite, and hematite. It is commonly found in sedimentary environments and bogs, where it accumulates in large deposits as “bog iron ore.”