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Download hereGENERAL DESCRIPTION
Goethite is an iron hydroxide, which is formed in iron-rich deposits, by weathering of minerals rich in iron (such as pyrite), in the hydrothermal marine deposits and by progressive recrystallization of the ferrihydrite ("rust" or "limonite" the old authors).
Goethite generally displays compact masses, botryoidal or stalactic, or with a dull and earthy habit. When occurring as compact masses, it takes a metallic dark color. Within matrixes, it constitutes also "limonite", an ochre yellow complex mixture primarily made up of ferrihydrite. When it is crystallized (what is definitely rarer), the crystals can be large-sized, measuring up to 45 cm. It can be associated to pyrite (FeS2), siderite (FeCO3), pyrolusite (MnO2)...
The deposits of goethite are very numerous throughout the world, but those which produced beautiful crystals are much fewer. Among the best, one will quote in particular: Siegen in Germany; the Restormel and the Botallack mines in England; the district of Pikes Peak and that of the Superior Lake in the United States.
In France, the deposits are also very numerous but a few produced remarkable samples: mines of Chaillac in Indre; the Sylvester and Donner mines in the Bas-Rhin; the mine of the Montmins in Allier, the Kaymar in Aveyron or Huelgoat in Finistère to quote only a few.
The place of conservation of the type of this species (originating in the district in Mesabi, Minnesota, the USA) is unknown.
HISTORY : Species dedicated to J.W von Goethe (1749-1832), German poet, naturalist and philosopher
Species first described in 1806 by Johann Georg Lenz, German professor of mineralogy (1745-1832)
Type-locality: Hollerter Zug, Kirchen Rheinland, Germany
CHEMICAL FORMULA : Fe3+ O(OH)
CRYSTAL SYSTEM : Orthorhombic
COLOR : Brown blackish, black
DIAPHANIETY : Opaque
LUSTER : Adamantine to metallic
STREAK : Yellow, orange, brown
MORPHOLOGIE : Prismatic and striated crystals. More often aggregates of acicular crystals
HARDNESS : 5,0 - 5,5
CHEMICAL CLASS: 4,18
DENSITY : IV - Oxides and hydroxides
GROUP : Diaspore
STRUNZ CLASS BEFORE 2001 : 4/F.06-30
STRUNZ CLASS AFTER 2001 : 4.FD.10
