XI. Class of Minerals

Tungsten and molybdenum compounds are natural salts of tungsten and molybdenum acids. Structurally, they are similar to phosphates and sulfates because their basic structural units are tetrahedral anion groups that do not bond with each other. Since tungsten and molybdenum ions are of similar size, they can substitute for each other in the mineral structure, leading to the formation of solid solution series. Although very rare in nature, minerals of this class are significant sources of tungsten and molybdenum. Among tungsten compounds, the most well-known are wolframite and scheelite, tungsten ore minerals, while among molybdenum compounds, wulfenite (lead molybdate) is notable.