Limonite (intermixed with Quartz/Goethite)
Limonite (generic term for hydrous iron oxides, primarily Goethite) · Mineral Specimen / Earthy Mineral / Ore Mineral
Crystal System
Amorphous or Orthorhombic (Goethite is orthorhombic); typically occurs as massive, earthy, or botryoidal crusts.
Mineral Group
Oxides and Hydroxides / Iron group
Chemical Formula
FeO(OH)·nH2O (primarily Goethite FeO(OH) with varying water content)
Formation Process
Sedimentary/Secondary: Formed by the weathering of iron-rich minerals (siderite, magnetite, pyrite) in oxidative environments near the surface.
About This Crystal
An earthy, yellowish-brown to dark brown crust with a dull to sub-metallic luster. It appears as an encrustation on a rock matrix, with some glistening vitreous micro-crystals that are likely quartz (SiO2) or secondary iron hydroxides.
Physical Characteristics
Color: Rusty brown to ocher yellow; Streak: Yellow-brown; Luster: Dull or earthy; Fracture: Uneven; Specific Gravity: 2.7–4.3; Non-fluorescent.
Optical Properties
Opaque; lacks refractive properties in massive form. Small associated quartz crystals may be vitreous and doubly refractive.
Hardness & Durability
Origin Region
Global (Australia, Brazil, USA, Germany); typically found in the gossan (oxidized cap) of iron-rich ore deposits.
Hardness & Durability
Mohs Hardness: 4.0 - 5.5 (varies significantly due to earthy texture). Brittle and prone to crumbling; low durability for jewelry.
Care & Maintenance
Keep dry; moisture can cause further oxidation or structural crumbling. Clean with a soft, dry brush; avoid water, chemicals, or ultrasonic cleaners.
Rarity & Value
Very Common; primarily valued as an iron ore or a collector specimen for its 'rusty' aesthetic. High availability leads to low market prices.
Special Characteristics
Can form pseudomorphs after other minerals like pyrite; may show iridescent 'rainbow' surfaces in certain botryoidal forms (turgite).
Lore & History
Historially used as a pigment (yellow ocher) for cave paintings and pottery. In traditional lore, it is considered a grounding stone associated with stability and protection.