S. L. Penfield — Crystal Drawing. 



63 



In _the combination observed on beryl, c (0001), m (1010), 

 jp (1011) and s (1121), figure 39, it takes considerable imagina- 

 tion to grasp the idea of the hexagonal shape and distribution 

 of the pyramidal forms from the clinographic projection alone, 

 relations which are at once brought out with distinctness by 

 means of the accompanying orthographic projection. In the 

 rhombohedral group of the hexagonal system clinographic 

 projections alone are at times quite inadequate for represent- 

 ing the shapes of crystals. For example, given the clinographic 



38 



3D 



40 



projection alone, figure 40, it may well be imagined that be- 

 ginners have difficulty in understanding the simple type of 

 calcite crystal represented, prism m, terminated by the flat 

 negative rhombohedron e (0112), but with the accompanying 

 orthographic projection, the hexagonal nature of the prism 

 and the distribution of the terminal faces about the vertical 

 axis with trigonal symmetry is evident. The two projections, 

 figure 41, supplement one another in giving an idea of the pro- 

 portions and arrangement of the faces observed on a crystal of 

 corundum from Cowee Creek, Macon Co., N. C. Figure 42 

 represents a crystal of hematite from Fowler, "N. Y., showing 

 the combination of the base c and a very flat rhombohedron x 

 (0'1'1'12). In this case the clinographic projection alone is quite 

 inadequate, for although the figure is a correct representation 

 in so far as the projection is concerned, it is next to impossible 

 to gain from it a correct conception of the shape and propor- 

 tions of the crystal which it is intended to represent. The 



