VEIN MINERALS. 223 



platy forms in association with purple fluorite, wolfram, oassiterite 



and molybdenite, 



Tho carbonate of calcium, calcito, CaCO^, has been obtained as a 

 vein mineral at Kanbauk only where it occurs 

 very rarely in tabular forma under the same 



conditions as siderite. Both i U<* carbonates are probably of secondary 



origin. 



White acicular crystals of eerussite, the carbonate of lead, 

 PbCOo, occur as a decomposition product on 



Cftn,ssifc0 - galena Eroro the Xatkyizin region. This 



mineral is of no economic importance in Tavoy. 



Fluorite or (luor sp ir, is the fluoride of calcium, ( ( aF 2 . Earlier 

 writer- have expressed the opinion that the 

 u ' llt0 ' mineral does not occur in Tavoy. but we have 



found that it has a wide distribution in small quantities. Amongst 

 other localities the following may be mentioned, Pagaye, where 

 green octahedra and colourless cubes occur in the pegmatites ; 

 Thingandon, as pale green, imperfectly Eormed crystals in the wol- 

 fram-bearing veins, and as amethystine films in (lie granite; Kanbauk. 

 as purple and green cubes from bearing veins in the sedimentaries ; 

 Paungdaw, as green cubical pieces in bearing veins in granite, etc. 

 It is an easy mineral to distinguish in the field by reason of its 

 colour, hardness (only ■!), specific gravity (3*2) crystal form, and 

 cleavage. 



Certain Silicates. 

 Topaz (A1F) 2 8i0 4 . According to J. -J. A.. I 'age, *" there is a 

 considerable amount of yellow topaz in some 

 Topaz ' of the veins, and also in the concentrate pro- 



cured by washing the alluvial deposits in various localities." With 

 the exception of the llermyingvi occurrence described later, we 

 have failed to find topaz in situ anywhere in Tavoy. A small 

 amount of water-clear topaz in grains and little, broken prismatic 

 crystals with worn edges, is contained in the crude cassiterite con- 

 centrates from the dredge at Taungthonlon. We are also indebted 

 to Mr. A. H. Morgan, who identified the mineral in minute quantities 

 in the concentrates of the Kamaunghla valley. We have recog- 

 nised the mineral occasionally when examining concentrates from 

 other streams, but we have no hesitation in saving that topaz is a 



1 J. J. A. Pago in discussion of Maxwoll-Lefroy'a paper (20), p. 113. 



E 



