Crystal Chemistry of Tungsten
Scheelite is an intermediate member of the complete homogeneous series of tungsten iron ore (FeWO4)-tungsten manganese ore (MnWO4). Theoretical Composition (ωB/%): tungsten iron FeO 23.65,WO376.35; tungsten manganese MnO 23.42,WO3 76.58. Those with a customary XFeWO4 greater than 80 per cent are called tungsten ores; those with XMnWO4 greater than 80 per cent are called tungsten and manganese ores; those between them are called wolframite. Common mixings are Mg、Ca、Nb、Ta、Sc、Y、Sn, etc. Among them, Nb、Ta、Sc can be replaced by homogeneous images, and more are micro inclusions.
The chemical composition of scheelite: CaWO4, because the radius of W and Mo ions in scheelite is almost equal, the W and Mo in scheelite are completely similar images and become scheelite —— molybdenum tungsten series. The crystals are nearly octahedral tetragonal double-cone, the aggregates are mostly irregular granular, less dense block. Colorless or white, usually gray, light yellow, light purple or light brown. Glass gloss to King Kong gloss, the fracture is grease gloss. the cleavage is medium and the fracture surface is staggered. Morse hardness 4.5~5. relative density 5.8——6.2(relative density decreases with increasing Mo). Light blue to yellow fluorescence under ultraviolet radiation.
