Formula: α-FeO(OH)
Origin of name: For J. van Goethe, German poet
Crystal system: Orthorhombic
Crystal class: 2/m 2/m 2/m
Twinning:
Unit cell: a = 4.608 Ǻ, b = 9.956 Ǻ, c = 3.021 Ǻ
Colour: Blackish brown, reddish or yellowish brown, brownish
Diaphaneity:
Luster: Adamantine-metallic to dull
Habit: Crystals prismatic, vertically striated, capillary or acicular in radiating clusters; massive radial, ocherous, colloform
Hardness: 5 to 5.5
Specific gravity: 3.3 to 4.3
Cleavage: 2; {010} perfect, {100} distinct
Tenacity: Uneven; brittle
Streak: Orange to brownish yellow
Synonyms/varieties: Allcharite, limonite (hydrated impure var.)
Comments: Polymorphous with akaganéite, feroxyhyte and lepidocrocite
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