MINERALS/Tungstates 587 eqn [1], and this explains the fact that tungstates with W in its highest oxidation state (ỵ6) dominate the mineralogy of the element in both the primary and the secondary environments WO24 ỵ 2H2 O ỵ 2e ! WO2 ỵ 4OH ẵ1 Tungstenite, WS2, is an extremely rare species, isomorphous with its common congener molybdenite, MoS2 Table provides a list of known naturally occurring tungstates The so-called tungstic acids of stoichiometry WO3 Á nH2O are not listed because they are simple lattice compounds However, due to possible confusion as to the attribution of certain species to the tungstate class, Table does include certain species that are in fact related For example, alumotungstite and ferritungstite are derivatives of WO3 with the pyrochlore structure Substitution of W by Al or Fe gives a positive charge discrepancy that is compensated by incorporation of other cations in a vacant lattice site In related fashion, raspite, PbWO4, the dimorph of stolzite, contains chains of edge-linked WO6 octahedra Pinalite, russellite, and tungstibite are complex layer structure oxides; cerotungstite-(Ce) and yttrotungstite-(Y) are complex secondary oxyhydroxide species containing chains of WO6 octahedra The same situation may obtain for Table Tungstate(VI) minerals Mineral Simple tungstates Ferberite Hubnerite Paraniite (Y) Raspite Sanmartinite Scheelite Stolzite Basic double salts Anthoinite Cuprotungstite Mpororoite Pinalite Russellite Tungstibite Complex uranium salts Uranotungstite Polytungstates Phyllotungstite Rankachite Other complex species Cerotungstite (Ce) Ferritungstite Alumotungstite Yttrotungstite (Y) Chemical composition MnWO4 FeWO4 Ca2Y(AsO4)(WO4)2 PbWO4 ZnWO4 CaWO4 PbWO4 WAl(O,OH)3(?) Cu3(WO4)2(OH)2 WAlO3(OH)3 2H2O(?) Pb3WO5Cl2 Bi2WO6 Sb2WO6 (Fe,Ba,Pb)(UO2)2(WO4)(OH)4 12H2O (Ca,Pb)Fe3H(WO4)6 10H2O CaFeV4W8O36 12H2O CeW2O6(OH)3 (W,Fe)(O,OH)3a (W,Al)(O,OH)3a YW2O6(OH)3 a Other cations, including Ca, Na, and Pb, may substitute in a site vacancy to compensate for charge imbalance (see text) anthoinite and mpororoite, two poorly characterized minerals that require further investigation Primary Tungstates All of the primary tungstates, including ferberite, huă bnerite, paraniite-(Y), sanmartinite, and scheelite, contain the simple WO24 ion Paraniite-(Y) and sanmartinite are both extremely rare minerals, but other members of the group have great economic importance, constituting the only minerals of tungsten to have value commercially Scheelite takes up molybdenum in the lattice and a complete solid solution extends to the isomorphous mineral powellite, CaMoO4 Primary scheelite, however, does not usually contain much molybdenum The term wolframite was formerly applied to members of the ferberitehuă bnerite series and the nomenclature is still commonly in use Solid solution in the series is in fact limited to about 20 mol% in each end-member and the separate end-member terms are now applied to individual specimens, depending on the exact composition Economically valuable deposits of the Alpine Cleft or sedimentary types of scheelite are well documented, but the main settings of scheelite, ferberite, and huă bnerite mineralization are either with acid-intrusive rocks or associated skarns Frequent associates of the tungstates are cassiterite, SnO2, molybdenite, MoS2, base metals such as copper, and minor amounts of gold Important mines were once located in all continents, but at present deposits in China, Indochina, and Brazil are the main sources of tungsten Secondary Tungstates Scheelite is also well known as a secondary mineral, especially associated with the oxidation of ferberite and huă bnerite In this setting, it also may incorporate molybdate in its lattice Other secondary tungstates are rare, with perhaps the most frequently encountered species being stolzite Notable locations of stolzite include the Clara mine and other mines in the Black Forest in Germany, and at Broken Hill and the Cordillera mine in New South Wales, Australia The Clara, Broken Hill, and Cordillera mines have produced raspite as a mineralogical curiosity and the latter is renowned for the association of the dimorphs with cuprotungstite As with molybdate (see Rocks and Their Classification), polymerization of tungstate in acid solutions yields polymeric species These are represented in the mineral kingdom by phyllotungstite and rankachite Both are much rarer than are their molybdenumbearing congeners and are of academic interest