12 
The upper geometrical figure shows the prism truncated on 
the three alternate vertical edges. The left hand figure 
below shows an hexaédral pyramid placed on the solid 
angles of the prism. The right hand figure shows facets 
that are on the horizontal edges and solid angles. The lower 
figure shows both ends, forming the alternating pyramid, 
giving four- and six- sided facets to the prism *. 
* It is remarkable that the pyramids in our erystals alternate with the 
faces of the prism, Hlatiy found them only opposite. 
