Mineral

Limonite (Iron Ore)

Limonite (an FeO(OH)·nH2O mineraloid, not a true mineral due to variable composition)

AI-generated identification · may be incorrect

Hardness: 4-5.5 on Mohs scale; Color: Brown, yellowish-brown, reddish-brown, dark brown; Luster: Dull, earthy, sometimes submetallic; Crystal Structure: Amorphous or cryptocrystalline, rarely forms distinct crystals (usually botryoidal, stalactitic, or massive); Cleavage: None; Specific Gravity: 2.7-4.3

Hardness: 4-5
Color: Brown, yellowish-brown, reddish-brown, dark brown
Luster: Dull, earthy, sometimes submetallic

Identified October 26, 2025More mineral →

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Physical properties

Formation & geological history

Limonite is a common secondary mineral formed from the hydration of iron oxides and hydroxides. It often results from the weathering and oxidation of iron-bearing sulfide minerals like pyrite or magnetite, and also from other iron-rich rocks. It can form in various environments, including swamps, bogs, and as a component of gossans (oxidized cap of an ore deposit). Its formation is ongoing in surface environments.

Uses & applications

Historically, Limonite was a significant iron ore, especially for early iron smelting. Today, it is less important as a primary iron ore due to lower iron content compared to hematite or magnetite, but it can still be used. It is also used as a pigment (ochre) and as a moderate abrasive. Some botryoidal or stalactitic forms are collected as mineral specimens.

Geological facts

Limonite is not a true mineral in the strictest sense because its composition is variable and it lacks a consistent crystal structure; rather, it is a mineraloid. It is often a mixture of hydrous iron oxides like goethite and lepidocrocite. The characteristic 'rust' color of many weathered rocks and soils comes from limonite.

Field identification & locations

In the field, Limonite can be identified by its distinctive brown to yellowish-brown streak (even if the specimen itself is dark brown), its earthy luster, and its relatively low specific gravity for an iron-rich material. It often forms as coatings or crusts on other minerals or rocks. It is commonly found in weathered iron ore deposits, bogs, and as concretions in sedimentary rocks. Collectors can look for well-formed botryoidal or stalactitic specimens.

Other mineral specimens

See all

Gneiss or Schist

Gneiss or Mica Schist with Garnet

Metamorphic

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

Pegmatite with Tourmaline and Quartz

Igneous Pegmatite

igneous

Granite

Granite (Phaneritic intrusive igneous rock)

igneous

Septarian Pebble

Septarian nodule / Concretion

sedimentary