ITS MODIFICATIONS. 



171 



and d y will generally incline on the adjacent primary 

 planes at unequal angles. 



The occurrence of modification b, alone, or modifi- 

 cation c, alone, or the unequal inclination of plane d, 

 or M, and T, will tend to distinguish the crystals 

 belonging to this class of prisms from those of the 

 square prism or cube. 



ITS MODIFICATIONS. 



Primary form. A right rhombic prism. 



The solid angles at A will be termed the obtuse, 

 and those at E the acute solid angles, of this class of 

 prisms. The edge G will be called the acute, and the 

 edge H the obtuse, lateral edges of the prisms. 



The individuals belonging to this class will differ 

 from each other in the inclination of M on M', or in 

 the ratio of the edge H to the edge B. 



Modifications. 



Class . Obtuse solid angles replaced by single 

 planes which intersect the terminal plane parallel 

 to its greater diagonal. 



When the planes a, increase so much as to meet 

 above the terminal plane, the resulting figure may 

 be an octahedron with a rectangular base, as shewn 

 in fig. 228. 



Fig. 228. 



