Rankachite Locality: Clara Mine, Rankach valley, Oberwolfach , Wolfach , Black Forest , Baden-Württemberg , Germany ( Locality at mindat.org ) Brown acicular xls of Rankachite, field of view 2 mm. Specimen and photo Leon Hupperichs. — Photo: Leon Hupperichs · CC BY-SA 3.0
Rankachite
Rankachite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula Ca₀.₅(V⁴⁺,V⁵⁺)(W⁶⁺,Fe³⁺)₂O₈(OH)·2H₂O.
It crystallizes in the monoclinic crystal system (space group Pmmn).
Key properties: Mohs hardness 2.5; specific gravity 4.03; Brown streak; Subadamantine to resinous, may be dull luster; optically biaxial.
IMA symbol Rka, IMA status: approved, named in 1983.
An alteration product of scheelite and iron sulfides in the oxidation zone of a hydrothermal base-metal deposit.
It is found associated with Scheelite, pyrite, marcasite, fluorite, barite, ferritungstite, quartz.
The name refers to the Rankach Valley, Germany, in which the Clara mine is located.