Limonite
Limonite (Hydrated iron oxide pseudomorph) · Mineral Specimen / Industrial Mineral
Crystal System
Amorphous or Cryptocrystalline; often occurs in massive, earthy, botryoidal, or stalactitic habits; frequently forms as pseudomorphs after cubic pyrite.
Mineral Group
Oxides / Hydroxides (Iron oxide mineraloid)
Chemical Formula
FeO(OH)·nH2O (Generic formula for a mixture of Goethite and other iron oxides)
Formation Process
Secondary process mineral; forms through the chemical weathering of iron-bearing minerals like pyrite, magnetite, and hematite in oxygenated, aqueous environments.
About This Crystal
An opaque mineraloid featuring a dull to earthy luster. It typically exhibits shades of mustard yellow, ochre, and dark rusty brown. The texture is often porous or granular, appearing as crusts or stains on a host rock matrix.
Physical Characteristics
Color: Yellow to dark brown; Streak: Yellowish brown; Cleavage: None; Fracture: Uneven to conchoidal; Specific Gravity: 2.7–4.3; Non-fluorescent under UV light; Brittle tenacity.
Optical Properties
Opaque; No significant birefringence or pleochroism; Refractive index is typically high (2.0-2.4) but difficult to measure due to opacity and texture.
Hardness & Durability
Origin Region
Worldwide; notable sources include Brazil, USA (Arizona), and Europe. Found in oxidized zones of iron-rich ore deposits and sedimentary bog iron.
Hardness & Durability
Mohs hardness: 4.0–5.5; Generally low durability; porous specimens can be crumbly and fragile; sensitive to acids.
Care & Maintenance
Keep dry to prevent further hydration or crumbly decay; clean only with a soft, dry brush; avoid ultrasonic cleaners, steam, and harsh chemicals.
Rarity & Value
Common; very low commercial value as a gemstone; primarily valued as a minor ore of iron or as a pigment (ochre); collectors value sharp pseudomorph specimens.
Special Characteristics
Notable for forming 'pseudomorphs' where it replaces the shape of another crystal (like pyrite) while retaining the original crystal's external form; used historically as the pigment 'Yellow Ochre'.
Lore & History
Used since prehistoric times as a pigment for cave paintings and body art. In metaphysical lore, it is believed to be a grounding stone that provides inner strength and assists in overcoming stagnation, often associated with the Root Chakra.