Limonite and Goethite
Goethite (alpha-FeO(OH)) with amorphous Limonite · Mineral Specimen / Industrial Iron Ore
Crystal System
Orthorhombic (Goethite) but typically displays a massive, earthy, or botryoidal habit
Mineral Group
Oxides / Hydroxides
Chemical Formula
FeO(OH)·nH2O (Variable mixture of hydrated iron oxides)
Formation Process
Secondary formation via oxidation and weathering of primary iron-rich minerals in soil and gosans
About This Crystal
The specimen shows an earthy to sub-metallic luster with a predominant rusty brown and ochre color. The texture is rough and massive with patches of darker goethite and yellowish limonite staining.
Physical Characteristics
Color: Yellowish-brown to dark brown; Streak: Yellow-brown/ochre; Fracture: Uneven/Conchoidal; SG: 2.7-4.3; Non-fluorescent
Optical Properties
Usually opaque (O); refractive index is high (2.26–2.51 for Goethite) but rarely measurable in massive forms
Hardness & Durability
Origin Region
Globally distributed; notable sources include Germany, Brazil, USA (Minnesota), and Cornwall, UK
Hardness & Durability
Mohs hardness: 4.0 - 5.5; Brittle tenacity; stable under normal conditions but can dehydrate to Hematite if heated
Care & Maintenance
Keep dry to prevent further hydration or alteration; clean with soft brush; avoid acids which may dissolve the iron content
Rarity & Value
Very common; low commercial value as a specimen unless displaying rare botryoidal iridescence (Turgite)
Special Characteristics
Known for forming pseudomorphs after other minerals like pyrite; may show slight iridescence in some botryoidal layers
Lore & History
Historically used as 'yellow ochre' pigment for cave paintings; traditionally associated with grounding and stability in lore