mineral

Limonite (Pseudomorph after Pyrite/Marcasite)

Hydrated Iron Oxide (FeO(OH)·nH2O)

AI-generated identification · may be incorrect

Hardness: 4-5.5 (Mohs); Color: yellowish-brown to deep ochre; Luster: dull, earthy, or sub-metallic; Crystal structure: Amorphous or microcrystalline; Cleavage: none; Specific gravity: 2.7-4.3.

Hardness: 4-5
Color: yellowish-brown to deep ochre
Luster: dull, earthy, or sub-metallic

Identified March 7, 2026More mineral →

Explore Limonite (Pseudomorph after Pyrite/Marcasite) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 4-5.5 (Mohs); Color: yellowish-brown to deep ochre; Luster: dull, earthy, or sub-metallic; Crystal structure: Amorphous or microcrystalline; Cleavage: none; Specific gravity: 2.7-4.3.

Formation & geological history

Formed through the oxidation and hydration of iron-rich sulfide minerals (like pyrite) in the weathering zone of ore deposits. This specimen appears to be a 'pseudomorph,' where limonite replaced a precursor mineral's crystal shape, likely during the Holocene to Pleistocene epochs.

Uses & applications

Historically used as a major iron ore and as a natural pigment (ochre) for paints. In modern times, it is primarily a minor ore and a specimen for mineral collectors.

Geological facts

Limonite is not a true mineral but a mixture of related hydrated iron oxides. It was the source of 'yellow ochre' used in prehistoric cave paintings, such as those in Lascaux, France.

Field identification & locations

Identify in the field by its characteristic yellow-brown streak (produced by scratching it against unglazed porcelain), its heavy weight for its size, and its earthy smell when damp. Common in bog iron deposits and oxidized caps of sulfide mines.