Goethite (with Limonite)
Goethite (Iron Hydroxide) · Mineral Specimen / Industrial Iron Ore
Crystal System
Orthorhombic; Habit is commonly botryoidal (grape-like), massive, stalactitic, or earthy rather than distinct crystals.
Mineral Group
Oxides / Hydroxides
Chemical Formula
α-Fe3+O(OH) [Often associated with hydrated iron oxides FeO(OH)·nH2O]
Formation Process
Secondary mineral formed through the weathering and oxidation of iron-rich primary minerals (like pyrite or magnetite) in soil and ore deposits.
About This Crystal
The specimen shows an opaque, dark brownish-black to black surface with a sub-metallic to vitreous luster. It features a botryoidal to massive texture with yellowish-brown to rust-orange earthy coatings (Limonite).
Physical Characteristics
Color: Dark brownish-black; Streak: Yellowish-brown; Cleavage: Perfect on {010}; Fracture: Uneven to conchoidal; Specific Gravity: 3.3–4.3; Non-fluorescent.
Optical Properties
Usually opaque. In thin sections, it can be anisotropic with high refractive indices (approx. 2.26) and strong pleochroism in shades of yellow and brown.
Hardness & Durability
Origin Region
Globally abundant, notably from Minas Gerais, Brazil; Tharsis, Spain; and Cornwall, England. Found in gossans (oxidized caps of ore deposits).
Hardness & Durability
Mohs hardness: 5.0–5.5; Brittle tenacity. Fairly durable but can be scratched by quartz or steel; porous varieties are prone to crumbling.
Care & Maintenance
Clean with a soft, dry brush; avoid ultrasonic cleaners and acids (which can dissolve the iron oxides). Keep in a dry environment to prevent further oxidation or hydration changes.
Rarity & Value
Common; Value is generally low for massive specimens, though iris goethite or aesthetic botryoidal 'velvet' specimens can command collector prices from $20 to $200+.
Special Characteristics
Specimen exhibits limonite encrustation (the orange-ochre areas) and a characteristic 'bubbly' botryoidal growth form common in iron-oxide gossans.
Lore & History
Historically used as 'yellow ochre' pigment for cave paintings dating back thousands of years. In metaphysical lore, it is believed to be a grounding stone that aids in connection to the Earth and processing grief.