2] 4 BROWN & HERON: GEOLOGY AND ORE DEPOSITS 01' TAVOY. 



The hydrous tungsten oxide, or tungsten ochre, is the yellow 



„, mineral left by the decomposition of wolfram 



Tungstito. it tit • 



or scheehte. Most lavoy veins contain sul- 

 phides ; these readily decompose and yield acid solutions by which 

 the wolfram is attacked. The final residue is the yellow tungstite 

 and it is found in all veins carrying wolfram in those parts through 

 which ground waters can circulate. The actual yellow tint' of the 

 mineral may vary a great deal from pale to orange. According 

 to Morrow Campbell " Its structure is usually porous as if it is 

 incapable of occupying the whole space of the original wolfram. 

 The reticulation it usually displays in section under the microscope 

 or even on polished surfaces shows wry plainly how decomposition 

 started from cracks and cleavage planes gradually extending in- 

 ward. Examples of the process in progress are common but large 

 masses of tungstite are rare on account of the facility with which 

 it is dissolved by alkaline solutions when it passes away as soluble 

 alkaline tungstate and is usually lost." Morrow Campbell goes 

 on to state that " if such a solution however encounters acid water 

 it is at once decomposed and hydrated tungstic oxide or tungstic 

 acid, the mineral known as meymacite is found. 1 But T. L. Walker 

 has shown that water is a normal constituent of tungstite and that 

 Carnot's " meymacite " is not a new mineral 2 so that Morrow 

 Campbell's meymacite must be regarded as tungstite. As he says 

 "It is quite commonly found in cavities and exists in two forms : — 

 (1) as sulphur yellow, moss-like tufts of radiating crystals, and, 

 (2), as small but often well-developed amber coloured crystals com- 

 monly single, sometimes in groups." 



Owing to its friability and the ease with which it decomposes 

 tungstite is of no economic importance in Tavoy. It is universally 

 distributed in the upper portions of veins, but is quickly carried 

 away by the tropical rainfall. 



The hydrous copper tungstate, which has the formula CuW0 4 , 



Uupiotungstito. 2H * ' is Said t0 haVe a bri g ht yellowish- 



green colour. It is a secondary mineral formed 



apparently by the alteration of scheelite. Its existence has not 



been definitely confirmed in Tavoy, though there is some reason to 



suppose that it may occur, as copper minerals are common enough in 



1 J. Morrow Campbell (9). The numerals refer to the bibliography, p. 9. 

 3 Walker, T. L. "A review of the minerals tungstite and meymacite." Ainer. 

 Jour. Sri., 4th ser., vol. 25, pp. 305-308, 1908. 



