TABLE OF SECONDARY FORMS. 



215 



planes, and e, or w, the lateral planes of a right 

 square prism. 



Secondary forms. 



How they may be derived. 



1. CONTAINED WITHIN FOUR 



PLANES. 



The regular tetrahedron . 



From the cube. Mod. g. 



2. CONTAINED WITHIN six 

 PLANES. 



The cube 



The right square prism 



The right rectangular 

 prism 



From the regular tetrahedron. 

 Modification e. 



regular octahedron. 



Modification a. 



rhombic dodeca- 

 hedron. Modification a. 



, right square prism. 



Modification d. The octa- 

 hedron with a square base, 

 by a concurrence of Modi- 

 fications a and e, or a and , 

 on the same crystal. 



, octahedron with a 



rectangular base, by the 

 concurrence of Modifica- 

 tions a, w, and o, on the 

 same crystal. 

 ...... octahedron with a 



rhombic base, by the con- 

 currence of Modifications 

 , ,, and w, on the same 

 crystal. 



, right rhombic 



prism, if Modifications f 

 and h occur on the same 

 crystal, and efface the la- 

 teral primary planes. 



