Goethite Nodules or Marcasite/Pyrite Nodule
Goethite (oxidized iron hydroxide) · Mineral Specimen
Crystal System
Orthorhombic; typically found in massive, reniform, botryoidal, or nodular habits
Mineral Group
Oxides and Hydroxides
Chemical Formula
FeO(OH)
Formation Process
Secondary formation via the weathering and oxidation of primary iron-bearing minerals like pyrite, marcasite, or siderite in low-temperature surface environments
About This Crystal
A small, rounded, spherical to nodular specimen with a dark brownish-black to rust-brown coloration, featuring an earthy to sub-metallic luster and a somewhat pitted or oxidized surface texture
Physical Characteristics
Color ranges from dark brown, yellowish-brown to black; streak is brownish-yellow or yellowish-brown; cleavage is distinct in one direction (rarely seen in massive forms); fracture is uneven; specific gravity is approximately 3.3 to 4.3; tenacity is brittle
Optical Properties
Opaque in hand specimen; refractive indices are high (approx. 2.26 to 2.40); biaxial negative; pleochroism is strong in thin sections
Hardness & Durability
Origin Region
Found globally; notable sources include USA, England, Germany, and Australia, often in weathered ore deposits
Hardness & Durability
Mohs hardness of 5.0 to 5.5; moderate durability, but can be brittle and sensitive to acidic solutions due to iron hydroxide composition
Care & Maintenance
Clean gently with a soft brush and warm soapy water; dry thoroughly to prevent further oxidation or rusting; store away from moisture and harsh acids
Rarity & Value
Common; widely distributed globally as an alteration product of iron ores; generally of low commercial value unless possessing exceptional crystal forms
Special Characteristics
Often forms as a pseudomorph after other minerals like pyrite, retaining the original crystal shape while completely transforming chemically into goethite
Lore & History
Historically used as a pigment (ochre) since prehistoric times for cave paintings; in modern metaphysical practices, it is believed to assist with grounding, emotional stability, and connecting to earth energies, though these are traditional beliefs and not scientifically validated