129 



as the pericline twins in plagioclase. The twin-axis is the 

 Ä-axis, One individual is placed behind the other, as shown 

 in figure 18. 



The combination of faces is somewhat varying, but gener- 

 ally very simple; the most common one, the one figured, is: 

 «{lOO}, è{0l0}, c{00l}, and м{Г01}. As the two cleavage- 



CL 



Fig. 15. Schizolite. Fis. 16. Schizol ite. 



•directions remain unaltered by the formation of twins, this for- 

 mation is only to be seen in developed crystals; otherwise it 

 would probably be seen much more commonly; of tolerably 

 complete crystals about the half is twins; from the other loca- 

 lities they have not been found. 



The twin-formation is seen, as shown in the figure, by 

 the fact that the face è{01u} on one side forms an out-going 

 angle, on the other side, exactly on the corresponding spot, a 

 XXVI. 9 



