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Download hereGENERAL DESCRIPTION
Rankachite is an hydrated calcium and iron vanado-tungstate. It forms as a result of the weathering of scheelite and iron sulphides, in polymetallic hydrothermal veins. Rankachite is frequently associated with scheelite, pyrite, marcassite and quartz.
The crystals of rankachite forms acicular groups of needles, arranged as spheres. Rankachite is opaque and of brown color.
Currently only one locality is known, the Clara mine in Germany (Black Forest). No mine is therefore known yet in France.
The type is kept at the National Museum of Natural History of Washington, USA.
Did you know? It is difficult to say if rankachite is rather a mineral of the phosphate-arsenate-vanadate family or a mineral of the tungstate-molybdate family because rankachite contains both tungstate and vanadate moieties. According to Dana, rankachite is more a tungstate when Strunz calssifies it as a phoshpate-aresenate-vanadate. This clear shows that those chemical classification of minerals are otfen odd and obsolete, especially when vanadates and molybdates have many chemical and structural features in common.
HISTORY : Named after its type-locality : Rankach
Species described in 1984 by Kurt Walenta (1927-), German mineralogist and Pete Dunn (1942-), American mineralogist
Type-locality : Mine Clara, Rankach, Baden-Wurttemberg, Germany
CHEMICAL FORMULA : Ca Fe2+ V5+4 W6+8 O36 12H2O
CRYSTAL SYSTEM : Orthorhombic
COLOR : Dark brown to yellowish brown
DIAPHANIETY : Opaque to translucent
LUSTER : Sub-adamantine to resinous
STREAK : Brown
MORPHOLOGIE : Elongated crystals, needles
HARDNESS : 2,5
CHEMICAL CLASS: 4,55
DENSITY : VII -Tungstates
GROUP : Rankachite
STRUNZ CLASS BEFORE 2001 : 7/C.34-10
STRUNZ CLASS AFTER 2001 : 7.GB.25
