TUNGSTEN MINERALS. 211 



is often shown. The wolfram from M. Sooratee s Winwa mine 

 is the most fibrous that we are acquainted with. 



(4) Columnar forms are merely** a variation of the preceding, 

 and seem to be a coarser development of the polysynthetic twinning 

 which gives rise to the fibrous variety. Good examples come 

 from Hermyingyi. 



(5) We give the term " acicular '" to those specimens of ore in 

 which long and very thin individual wolfram crystals are scattered 

 indiscriminately through the quartz matrix. The best examples 

 come from Mr. T. Fowle'e Yanmazu North mine. 



For the benefit of prospectors it may be stated that the specific 

 gravity of wolfram varies between that of hiibnerite and that of 

 ferberite, from 7'2 to 7*5, that its hardness is about 5 and that its 

 streak is dark reddish-brown to dark brown. Though nearly always 

 black in colour, Tavoy wolfram may assume a brownish appearance 

 when stained by iron minerals, and, very rarely, dark grey varieties 

 are met with. Especially characteristic is the very perfect cleavage 

 of the mineral parallel to the long axis of the crystal. Rounded 

 pieces of wolfram, which may be disguised by coatings of oxides of 

 iron and manganese, always show this when broken open. There 

 are other cleavages in the mineral but they are of no determinative 

 value in the field. Finally, wolfram has a submetallic lustre, 

 is opaque and brittle. 



In thin sections under the microscope patches of a deep red colour 

 are sometimes seen, set in the opaque ground-mass. Ferberite in 

 extremely thin sections, probably not more than 0-0001 or 0-0002 

 inch thick, is said to be red, while hiibnerite is typically reddish- 

 brown, or even dark green in section. 1 How far the colour seen 

 in some sections of Tavoy wolfram is due to original variations 

 of composition in the same parts of the same section or how far 

 it is due to changes brought about by leaching of the iron or manga- 

 nese, or both, is not known. 



Calcium tungstate, Ca\YO v The presence of this mineral in 



Tavoy concentrates was first brought to notice 



Schoehte. .^ ^^ ^y a magnetic separating firm in 



London, who detected it in the tin residues from Pagaye mine. 



It was not discovered in situ for some time afterwards, when the 



first specimens were found by Mr. A. H. Morgan, General Manager 



1 Hess, loc cit., pp. 22 and 25. 



