Tungsto-vanadosilicates

These complexes are analogous to the molybdo-vanadosilicates, and are prepared as yellowish-red to red crystals by the action of vanadates on the silico-tungstates, or by the action of hydrofluosilicic acid on the tungsto-vanadates. The following series has been recognised

3R₂O.SiO₂.V₂O₅.9WO₃ xH₂O;
3R₂O.SiO₂.V₂O₅.10WO₃.xH₂O;
7R₂O.2SiO₂.3V₂O₅.18WO₃.xH₂O.
(R = NH₄ or K; R₂ = Ba.)

Double salts have also been isolated.

Several of the natural ores of vanadium consist of complex silicates, e.g. ardennite and roscoelite.