46 CRYSTALLOGRAPHY. 
I. HEXAGONAL SECTION, 
1, Description of Forms.—Figs. 1 to 3 represent some of the 
forms under this section. Figs. 2 and 3 show only one ex- 

MIMETITE. BERYL. ; APATITE. 
tremity; and such crystals are seldom perfect at both. ATL 
exhibit well the symmetry by sixes which characterizes this 
section of the hexagonal system. . 

Prisms. Under this system there are two hexagonal prisms 
and a number of occurring twelve-sided prisms. Fig. 4 repre- 
sents one of the hexagoral prisms, with its axes—the three 
lateral connecting the centres of the opposite edges. The 
lateral angles of the prism are 120°. If the lateral edges of 
this prism are truncated, as in the figure of apatite (fig. 3), the 
truncating planes, 7-2, are the lateral faces of another similar 
hexagonal prism, in which, as the relations of the two show, the 
