CLEAVAGE. 





Fig. 86 exhibits the same rhomboid separately, the 

 planes being marked with the same letters as are 

 placed on such planes of the octahedron as are pa- 

 rallel to those of the included rhomboid. 



Fig. 87. 



Our rhomboid may thus be regarded as an imperfect 

 octahedron, two of its planes being concealed, or covered 

 by small tetrahedrons p r s, and t u x, as in figure 

 86. These tetrahedrons consist of masses of cubic 

 molecules, and by their removal, as in fig. 87, we 

 shall obviously reproduce the perfect octahedron. 



Fig. 88. 



If we now cleave the octahedron parallel to any 

 four alternate planes, as c d, ef, fig. 84, and continue 

 the cleavage as far as the lines i k, I m, no, fig, 88, 

 and until only the central points of the four planes 

 a, b, g, h, remain, we shall produce a regular tetra- 

 hedron, as shewn by the interior lines in the figure. 



