Greenish crystal agregates of the very rare tungsten oxide mineral tungstite from the famous Panasqueira deposit in Portugal. Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Hydrotungstite
Hydrotungstite is an IMA-recognized mineral species in the tungstate class, with the chemical formula WO₂(OH)₂·H₂O.
It crystallizes in the monoclinic crystal system (space group P2/m).
Key properties: Mohs hardness 2; specific gravity 4.6; Vitreous to dull luster; optically biaxial.
IMA symbol Htgs, grandfathered status — known before the IMA’s founding, named in 1944.
An alteration product of ferberite in the oxidized zone of a hydrothermal tungsten deposit, where it was an ore mineral (Calacalani mine, Bolivia).
It is found associated with Ferberite, tungstite.
The name refers to its content of H2O and relation to tungstite.