Limonite with Goethite (Bog Iron)
Goethite-Limonite Assembly · Mineral Specimen / Industrial Iron Ore
Crystal System
Amorphous (Limonite) / Orthorhombic (Goethite) with massive, botryoidal, or earthy habit
Mineral Group
Oxides / Hydroxides
Chemical Formula
FeO(OH)·nH2O (Variable mixture of hydrated iron oxides)
Formation Process
Secondary formation through the oxidation and hydration of iron-rich minerals (like pyrite or magnetite) in sedentary or weathering environments.
About This Crystal
An opaque, earthy to metallic specimen showing a range of yellow-ochre to dark brown/black colors. Luster varies from dull/earthy to sub-metallic or silky where crystallized grains are present.
Physical Characteristics
Color: Yellowish-brown to black; Streak: Yellowish-brown; Cleavage: None; Fracture: Uneven to conchoidal; Specific Gravity: 2.7–4.3; Fluorescence: None.
Optical Properties
Opaque; No significant birefringence or refractive index measurable in massive form; non-pleochroic.
Hardness & Durability
Origin Region
Worldwide; notable deposits in Minas Gerais, Brazil, and the Lake Superior region, USA, typically in weathered iron-rich rocks.
Hardness & Durability
Mohs hardness 4.0 - 5.5; Brittle tenacity; generally stable but can be porous and susceptible to internal fracturing.
Care & Maintenance
Avoid harsh acids which can dissolve the iron content; clean with dry brushes or lukewarm water; store in a low-humidity environment to prevent further hydration or crumbly degradation.
Rarity & Value
Common; primarily valued as iron ore or as display specimens for iridescent varieties (iridescent goethite / turgite), generally low market value for earthy specimens.
Special Characteristics
Often forms pseudomorphs after other minerals (like pyrite cubes); may show iridescent 'oil-slick' colors on certain surfaces due to thin-film interference.
Lore & History
Historically used as a primary source of yellow and brown ochre pigments for cave paintings and pottery; traditionally associated with grounding, physical stamina, and protection in folk lore.