VEIN MINERALS. 215 



some localities and are known to decompose readily. Maxwell 

 Lefroy has mentioned the occurrence of " metallic green and 

 yellow wolfram ochre stains or accretions on quartz — massive or 

 crystalliform in cavities from which they were derived." 1 



This mineral has not been identified in Tavoy but there is no 

 reason why it should not occur. The follow- 

 ing description is taken from Hess's work. 2 



'• Ferritungstite, hydrous ferrous tungstate (Fe 2 ;r W0 3 , 6H 2 0), 

 is a light yellow mineral much paler than tungstite. It is friable 

 or powdery and looks very much like iron stained clay. Under 

 the microscope it is seen to be made up of small hexagonal plates. 

 It has been found only as a product of the decay of wolframite, 

 and, like tungstite, may be left in spaces from which wolframite 

 has been weathered, and it may thus show the prospector that other 

 tungsten minerals lie below the weathered outcrop." 



Some of the light powdery varieties of the Tavoyan " tungstite " 

 may prove to be ferritungstite on proper examination. 



Tin oxide (Sn0 2 ), nearly always accompanies wolfram in Tavoy 



veins, the two minerals are found together in 



the detrital deposits, and, of the two, cassiterite 



is found alone in the true river-sorted alluvial sands and gravels. 



The mineral is unequally distributed throughout the district 

 and veins in granite usually carry more tin-stone than do those in 

 sedimentary rocks. There are however certain exceptions to this 

 rule. It also occurs in true pegmatites. The mines producing 

 most tin- stone are those at the northern end of the Central Range, 

 viz., Hermyingyi, Taungpila and Pa-in. 



The mineral is found in a great variety of forms and colours. 

 The commonest shades are browns and greyish-browns, but cassiterite 

 of white, grey, pink, chocolate, ruby red and black tints also occurs. 

 The fine granular varieties met with in alluvial deposits exhibit 

 every shade of yellow, brown and red to black. 



The cassiterite of the Pagaye pegmatites occurs usually as imper- 

 fectly formed pyramidal crystals of a light greyish-red colour and 

 is often associated with green fiuorite. Narrow veinlets in the 

 south extension of the stockwork at the same mine are sometimes 

 filled completely with dark greyish-black pyramidal cassiterite and 

 a white mica. 



1 E. Maxwell Lefroy (20), p. 3. 

 i Loc. cit., p. 34. 



