66 



S. L. Penfield — Crystal Drawing. 



In this case the revolution about the vertical axis is 28° 26' 

 instead of 18° 26', as in the previous illustrations, and both 

 terminal faces are thus shown in the lower figure. By means 



49 50 



51 



II 



III 



tion of the b axis, showed only 



of the axial protractor, page 

 44, it is an easy matter to 

 plot the axes in the position 

 chosen. 



Owing to foreshortening, 

 without the use of an ortho- 

 graphic projection it often 

 becomes a very difficult 

 matter to construct a figure 

 in clinographic projection 

 in which the relative pro- 

 portions of the several faces 

 of a crystal are preserved 

 with accuracy. A case 

 illustrating this, encoun- 

 tered in the study of some 

 very beautiful and complex 

 crystals of azurite from 

 Broken Hill mines, New 

 South Wales, figure 51, 

 may be cited. The drawings 

 were made by Mr. R. G. 

 Yan Name when a student 

 in the writer's laboratory. 

 The crystals, lengthened 

 like epidote in the direc- 

 one termination, and the 



clinographic projection III represents the crystal turned 



