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Goethite (Photo) [abbr. Gth ]

Year of discovery: 1806 (Hollertszug mine, Germany), 1930 (Japan)

Locality list: 318 localities of goethite

• FeO(OH)
• α-[Fe³⁺][OH|O]^3-
• A component of Limonite

• Class: Diaspore group
• Class: Oxide - Hydroxide
• Soluble in: HCl
• Magnetism: Paramagnetic (After heating)
• Phase transition: Formed on transition of Feroxyhyte.
• Substitution pseudomorph: Replace Siderite, Pyrite, Baryte, or Calcite.

• Polymorph: Akaganeite (β, Monoclinic), Lepidocrocite (γ, Orthorhombic), Feroxyhyte (δ, Hexagonal)

• Fe => Al: Diaspore (α), Böhmite (Bohmite) (γ)
• Fe => Mn: Groutite (α), Feitknechtite (β), Manganite (γ)
• Fe => V: Montroseite
• Fe => Cr: Guyanaite, Bracewellite
• Fe => Ga: Tsumgallite
• Fe => Co: Heterogenite

• Color: Reddish brown, Yellowish brown, Dark brown
• Streak: Yellowish brown
• Luster: Adamantine
• Diaphaneity: Opaque

• Habit: Acicular
• Aggregate: Radial, Reniform

• Cleavage: Perfect on {010} (1 plane), Distinct on {100} (1 plane)
• Hardness: 5-5.5
• Density: 4.3

• System: Orthorhombic
• Group: mmm, Pbnm
• Lattice: a=4.6, b=10.0, c=3.0

Etymology: Goethe, German literary arts writer

Synonym: Hydrohematite