220 BROWN & HERON: GEOLOGY AND ORE DEPOSITS OF TAVOY. 



The mineral is easily confused with graphite but the mark 

 it leaves on paper ha* more of a greenish tint than that left by 

 graphite. 



Molybdenite is readily attacked by acid solutions with the 

 production of the oxide moh/hdile, which is a pale yellow soft mineral 

 occurring in the spaces left by the molybdenite, as silky tufts or as an 

 earthy powder. 



The yellow sulphide of iron, FeS 2 , is common everywhere. 

 Its cubic crystals and pale brass-yellow colour 

 are so well known that it seems unnecessary 

 to give any further tests to help the prospector to distinguish it. 

 Yet it has been mistaken for chalcopyrite and for pyrrhotite. It is 

 distinguished from the former by its greater hardness, its paler 

 colour and from the latter by its colour. Pyrrhotite is of a pinch- 

 beck-bronze tint and is also slightly magnetic. Pyrite is not only 

 a very frequent mineral in the metalliferous veins, where it is generally 

 found in lustrous cubes and growths of cubic combinations, but it 

 also occurs in the pegmatites, in the granites and in the slates of 

 the Mergui Series, especially when these are near the granite con- 

 tacts. Massive pyrite and intergrowths of the mineral with chal- 

 copyrite are also of common occurrence. The mineral is very easily 

 decomposed and some varieties, probably because they contain 

 marcasite, decompose more quickly than the others. When these 

 changes take place ferrous sulphate and sulphuric acid are formed. 

 It is believed that the sulphuric acid so liberated is to a large extent 

 responsible for the removal of wolfram from the upper parts of 

 veins through which ground water circulates. 



The copper-iron sulphide, chalcopyrite, CuFeS 2 , a bright brassy- 

 yellow mineral which crystallizes in the tetra- 

 gonal system is. after pyrite, the commonest 

 sulphide ore in the district. It is distinguished from pyrite in the 

 field by its colour and its softness, being easily scratched with a 

 knife. On exposure to the air it readily tarnishes and then assumes 

 the iridescent colours which give it the name of " peacock copper." 

 The best specimens come from the Pagaye pegmatites, from the lower 

 workings at Kanbauk and from Kadando, where it is found with 

 pyrrhotite in a wolfram-bearing vein, but it was formed later than 

 the wolfram as it fills cracks in that mineral. It also occurs at 

 Egani and in small quantities at Hermyingyi. 



