Limonite / Goethite (Ironstone)
Hydrous Iron Oxide (mainly Goethite) α-Fe3+O(OH) · Mineral Specimen / Industrial Ore
Crystal System
Orthorhombic; typically found in massive, botryoidal (grape-like), or earthy habits.
Mineral Group
Oxides / Hydroxides
Chemical Formula
FeO(OH)·nH2O
Formation Process
Secondary mineral formed by the weathering and oxidation of iron-rich minerals (like pyrite) in sedimentary or hydrothermal environments.
About This Crystal
An opaque, earthy to sub-metallic specimen with a dark brown to yellowish-brown color. It features a bumpy, botryoidal surface texture and a dull to waxy luster.
Physical Characteristics
Color: Dark brown to ochre yellow. Streak: Yellowish-brown. Cleavage: None. Fracture: Uneven to conchoidal. Specific Gravity: 2.7–4.3. Non-magnetic unless heated.
Optical Properties
Opaque (no light transmission). Under microscope: Adamantine/sub-metallic luster on fresh breaks. No pleochroism visible in hand specimen.
Hardness & Durability
Origin Region
Worldwide; notably from sedimentary iron formations in the USA (Minnesota), Germany, and Australia.
Hardness & Durability
Mohs hardness: 4.0–5.5. Brittle tenacity; generally stable but can be friable if earthy.
Care & Maintenance
Clean with a soft brush and warm water. Avoid acids (hydrochloric acid dissolves it) and ultrasonic cleaners if the specimen is porous.
Rarity & Value
Very common. Value is generally low, primarily of interest as an industrial iron ore or for collector specimens with unique botryoidal formations.
Special Characteristics
Botryoidal (globular) surface texture and 'pseudomorph' capabilities where it replaces other minerals while retaining their original shape.
Lore & History
Historically used as 'yellow ochre' pigment for cave paintings and pottery. Traditionally associated with grounding, physical strength, and mental focus.