194 R. H. Rastall — The Genesis of Tungsten Ores. 



standard textbooks are not very satisfactory. Mr. A. M. Finlayson ^ 

 has briefly discussed the genesis of the ores from a theoretical point 

 of view in the Geological Magazine for 1910, giving a large number 

 of references, and in 1909 the Imperial Institute published a small 

 monograph on the subject fi'om the practical standpoint,^ but no 

 general account of recent date seems to be available. 



The element tungsten does not enter into many compounds of 

 natural occurrence. It belongs to the group of metallic elements 

 that give rise to acid-forming oxides ; tungstic acid forms salts with 

 several divalent metals, especially iron, manganese, calcium, and lead. 

 The tungstates of these metals fall into two well-defined groups; 

 the iron and manganese minerals crystallize in the monoclinic 

 system, while the others are tetragonal. So far as is known tungsten 

 does not occur in nature as sulphides or anhydrous oxides; even the 

 oxidation products of the tungstates are few in number, the only one 

 that is at all common is tungstic ochre, a yellow powdery substance 

 sometimes found as a crust on tungstate minerals. It appears to be 

 a hydrated oxide or hydroxide of a not very definite composition. 

 The tungstates are remarkably stable minerals, being little affected 

 by any weathering agents, and in consequence the ores do not 

 undergo secondary enrichment; on the other hand, they show 

 a strong tendency to accumulate as shoad and alluvial deposits. 



The iron and manganese tungstates, commonly known collectively 

 to the miner as wolfram, form an excellent example of an isomorphous 

 series. The two theoretical end-products are ferberite, FeWO^, and 



^ Finlayson, " The Ore-bearing Pegmatites of Carrock Fell " : Geol. Mag., 

 1910, p. 19. 



2 "The Occurrence and Utilization of Tungsten Ores" : Bull. Imp. Inst., 

 vol. vii, pp. 170, 285, 1909. 



