Limonite (Iron Stone)
Iron Oxide-Hydroxide mixture (principally Goethite) · Mineral Specimen / Industrial Mineral
Crystal System
Amorphous or Cryptocrystalline; found in massive, earthy, or botryoidal habits.
Mineral Group
Oxides / Hydroxides
Chemical Formula
FeO(OH)·nH2O
Formation Process
Secondary formation via the oxidation (weathering) of iron-rich sulfide minerals or precipitation from bog water.
About This Crystal
An opaque, earthy to sub-metallic specimen with a dull luster. It displays a yellowish-brown to dark rusty brown color and a rugged, uneven surface texture.
Physical Characteristics
Color: Yellow-brown to dark brown; Streak: Yellowish-brown; Cleavage: None; Fracture: Uneven/Conchoidal; SG: 2.7–4.3; Fluorescence: None.
Optical Properties
Opaque; No refractive index (amorphous); lacks pleochroism or dispersion; dull optical response.
Hardness & Durability
Origin Region
Worldwide; notable deposits in Minas Gerais, Brazil; Lorraine, France; and the Lake Superior region, USA.
Hardness & Durability
Mohs hardness: 4.0–5.5; Brittle toughness; relatively stable but can be porous.
Care & Maintenance
Avoid acidic cleaners; clean with a soft dry brush; store in a dry environment to prevent further hydration changes.
Rarity & Value
Very common; low commercial value for small specimens; primarily valued as an iron ore or pigment source.
Special Characteristics
Often forms pseudomorphs after other minerals like pyrite; used historically as 'yellow ochre' pigment.
Lore & History
Historically used as one of the first pigments for cave paintings. Metaphysically associated with grounding and stability (Root Chakra).