216 BROWN & HERON: GEOLOGY AND ORE DEPOSITS OF TAVOY 



At Yanmazu, grey and dark grey crystals showing both pyramidal 

 and stout prismatic forms are deposited on the mica walls of narrow 

 veinlets. 



Hermyingyi cassiterite is characterized by its peculiar light 

 brown shades and coarse imperfect crystals. 



Massive cassiterite, forming solid ore built up of intergrowing 

 crystals, occurs as veinlets in greisen at the Pa-in mine. These 

 veinlets vary from one inch to 6 inches in thickness and often yield 

 masses up to 100 lbs. in weight. Large crystals of brown and black 

 cassiterite are also found there and often a whole suit ! of colours 

 s to b i observed in an individual crystal. 



The finest specimens como from Taungshuntaung, where black 

 bi-pyramidal forms with a splendent lustre are found on mica 

 rock with crystallized quartz. 



The druses sometimes met with in the lodes at Kanbauk furnish 

 beautiful and distinctive specimens of quartz crystals intergrown 

 with wolfram and deeply implanted with small shining black crys- 

 tals of cassiterite. Especially interesting is a specimen in the 

 possession of Mr. W. Leslie of a tabular wolfram crystal broken 

 across its short axis and held together by two crystals of cassiterite 

 which have grown on the fracture. It is impossible to describe 

 the endless mutations which cassiterite presents in Tavoy. The 

 remarks already made relate to the mineral in its crystalline form 

 and it remains to say that such crystals are always imperfect, very 

 often intergrown with other individuals, and more often than not 

 twinned either by contact or penetration. The knee-shaped doubt- 

 let twins are very common. 



The mineral is also found in irregular aggregates which mav 

 show a tendency towards botryoidal structure or have imperfect 

 crystal forms and impressions on the surface. It then possesses 

 a roughly radial structure with concentric band< and under the 

 microscope shows irregular aggregate polarization. This form is 

 very brittle. 



Small slender prisms of shining black cassiterite terminated bv 

 very acute pyramid faces resembling the sharpened point of a lead 

 pencil, occur at the Seinpyon mine near Natkyizin in the north 

 of the district. They have been called " needle tin." The 

 squatter piismatic forms terminated by the pyramid are also found 

 there. 



