194 



THE ROYAL SOCIETY OF CANADA 



usual milky white variety, through which, in addition to the minerals 

 mentioned above as generally occurring in these veins, there are 

 distributed patches of dark green, massive or fine-granular chlorite. 



The phenacite, in the specimen collected, is intimately associated 

 with the latter mineral. For the most part it is massive, or exhibits 

 an ill-defined prismatic habit. In appearance it closely resembles 

 the quartz, than which, however, it is rather more colourless and 

 transparent. The similarity to quartz is further increased by the 

 hexagonal form and optically positive character, but the birefringence 

 and high refractive index proved conclusively that the mineral could 

 not be quartz. A few imperfectly terminated crystals were found, 

 and from the measurement of these, the mineral was identified as 

 phenacite. The following forms were observed on the crystals: — 

 a(1120), m(lOÎO), /^(5Ï40), KlOÎl), /'(1123), ^i(2ÎÎ3), (/(01Î2). 



On one crystal, of which figure 3 is a drawing, there is, in addition 

 to the above forms, a well-defined face lying betwen r(lOll) and 



Figure 3. 



^(1123), but not quite in zone with them. This is vicinal, but very 

 nearly coincident with z'(2134), as may be seen from a comparison of 

 the measured and calculated angles: — 



Angle Measured Calculated 



63° 44' 

 72° 50' 

 14° 32' 



The prism is striated vertically, while on the face a(1120) there 

 are also striae parallel to the edge ar. 



The crystals have a diameter of about 2 mm., and only about the 

 same length of prism, bearing the terminating forms, stands out 

 freely from the massive matrix. The latter is itself largely phenacite, 

 often showing an ill-defined, longitudinally striated prismatic form, 



