192 THE ROYAL SOCIETY OF CANADA 



position; one of these, however, (that on the right in the figure), is 

 molybdenite, while the other is composed of bismuthinite. Neither 

 individual has a very sharp crystal outline, but each presents the 

 appearance of a hexagonal bi-pyramid with its apices deeply truncated 

 by faces of the basal pinacoid, so that the habit is somewhat 

 tabular. 



In the molybdenite crystal, the pyramid faces are, as is usual, 

 heavily striated parallel to the base; it would be more correct to say 

 that the pyramid is formed by the free outer edges of superposed thin 

 plates of molybdenite, which, being of continually decreasing diameter, 

 give rise to the tapering above and below. Approximate measure- 

 ment of the angles with the hand goniometer indicates that the pyra- 

 mid is the form o(lOÎl). Instead of a flat basal plane, the upper 

 surface of the crystal exhibits a concave rosette form, due to the man- 

 ner in which the hexagonal plates, of smaller and variable size, overlap 

 here, and also in part to a curvature of the plates. The crystal is 

 coated in places with a little earthy yellow molybdite, but in general 

 this is inconspicuous or absent. 



The other individual (on the left in Fig. 1) shows the same com- 

 bination of pyramid and basal pinacoid, and has similar angles; but in 

 this case the base is an approximately flat surface. It is composed of 

 very fine-granular bismuthinite, through which occasional specks of 

 native bismuth, isolated or in small nests, are dispersed. Here and 

 there, also, traces of the original molybdenite may be seen. The 

 surface is largely coated with a thin deposit of greyish-white or 

 yellowish-white material, which is, in part at least, bismuth carbonate. 



The manner in which the replacement of the molybdenite by 

 bismuthinite has progressed may be observed better on the under side 

 of the specimen. Attached to the large molybdenite crystal are 

 several smaller crystals of similar habit, which also are quite fresh 

 and unaltered. Below the pseudomorphous individual, on the other 

 hand, are some crystals which show partial alteration to bismuthinite. 

 One of these has been broken across and shows in cross-section the 

 curvilaminar structure resulting from the superposition of curved 

 flakes. At one end of this crystal the molybdenite has been entirely 

 replaced by bismuthinite, but the original structure is still very evident. 

 The fine granular bismuthinite retains the form of the curved plates, 

 and in some cases these are easily separable, owing to the presence 

 of a thin film of oxide, or of molybdenite, between them. Even 

 where the material is more compact, the original curvilaminar structure 

 is plainly indicated by a streaky appearance, largely caused by the 

 presence of narrow streaks of earthy grey oxidation products, in part 

 bismuth carbonate. Another portion of the same crystal is still 



