216 



TABLE OF SECONDARY FORMS. 



Secondary forms. 



The right rhombic prism . 



The right oblique-angled 

 prism 



How they may be derived. 



From the octahedron with a 

 rectangular base, by the 

 concurrence of Modifications 

 a and e, or a and / ? or a 

 and g, on the same crystal ; 

 or of b and o, or n and o, in 

 which case o would appear 

 a terminal plane ; or of c 

 and m,or p and m, appear- 

 ing then as the terminal 

 plane. 



octahedron \vith a 



rhombic base, by the con- 

 currence of Modifications 

 a and i 9 or a and p, or a 

 and #, on the same crystal; 

 or of b and w, or h and w, 

 or t and n ; or of c and g-, 

 or o and g-, or v and g ; but 

 in these latter combina- 

 tions, n and g would ap- 

 pear as terminal planes. 



right rectangular 



prism. Modification c?; or 

 Modification &, or c, if we 

 suppose the planes &, or c, 

 to have effaced four of the 

 primary planes, and the 

 figure then rest on the plane 

 MorT. 



right rhombic prism, 



Modification g, or i. 



oblique rhombic 



prism, by the concurrence 

 of Modifications h and A:, on 

 the same crystal, and by 

 supposing the secondary 

 form to rest upon the plane 

 A:. In this position the 

 planes k would appear as 

 the terminal planes of the 

 new figure, and plane P as 

 one of the lateral planes. 



