140 



that otherwise characterizes the mineral is not found on this 

 individual. On the other hand, the form m has on this crystal 

 attained a development to which nothing corresponding is found 

 on the common leucosphenite crystals. The faces of the- form 

 y are large, smooth and of a magnificent lustre. The pinacoid 

 of the second order d is represented by a very small, but brilliant 

 and quite determinable face. The face a of the first pinacoid 

 is large , smooth and brilliant. The largest of the terminal 

 planes of this crystal, however, are those of the form s. They 

 belong to the zones [001, 110] and [Oil, 101], which is sufficient 

 for a certain determination of the form. 



The leucosphenite crystals of the common type are generally 

 developed on both ends. The faces of the third pinacoid are, 

 as a rule, striated longitudinally, which striation is due to the 

 alternation of faces belonging to the forms с and x. Some- 

 times the striation disappears, at least in places, and then 

 the face is dull. Some crystals are striated on one side and 

 dull on the other. When dull and striated spots occur on the 

 same faces, they border irregularly on one another. The faces 

 of the second pinacoid are also striated, but on them the stria- 

 tion runs in the vertical direction, consequently across their 

 longitudinal direction. Here it is the form n which causes 

 the striation by alternation. In most cases the striation is most 

 marked at the ends of the faces; the middle portions of the 

 faces generally have no striation. These faces are, besides, 

 seldom quite plane, but either show a continuous rounding or 

 an abrupt bending, owing to which their ends make a smaller 

 angle with n than the unbroken plane would make. The diffe- 

 rence I have found almost unvariably to be about 1° towards 

 each end. Also on the faces of the form n occurs a vertical 

 striation, which, however, does not essentially interfere with the 

 measurement of the angles. The crystals are not in general 

 very sharply developed, their edges and corners usually being 

 somewhat rounded off. Only the crystal represented by Fig. 9, 



