434 
Mr. G'reville on the 
and this cut or section forms an angle of 122°34/, with the 
pLne on the extremity. 
It is unnecessary to observe, that the regularity of the 
hexaedral prism, depends on that of the rhomboidal parallelo- 
piped on which it is formed. 
When, by detaching the laminae from the alternate solid 
angles of the regular hexaedral prism, the planes resulting from 
this operation begin to run into one another, and the crystal 
begins to assume the form of the rhomboidal parallelopiped to 
which it owes its origin, we frequently see the surface of these 
new planes divided into an immense number of small rhombs, 
formed thereon by the intersection of lines that are parallel to 
the sides, which belong to the rhomboidal form of the new 
faces. (Fig. 3.) 
These lines are owing to the extremities of the laminae which 
have been deposited on the inferior faces, corresponding with 
those on which we observe them; and they serve to corro- 
borate still farther, the demonstration we have given of the 
formation of the regular hexaedral prism in this substance. 
We frequently see small rhombs traced on the surface of 
the planes, on the ends of the hexaedral prism. (Fig. 10.) This, 
no doubt, is occasioned also by the intersection of the laminae, 
on the planes of the primitive rhomboidal parallelopiped. But 
these rhombs, formed by the re-union of lines that join in angles 
of 6 o° and 120°, instead of 86° and 94 0 , (like those we have 
seen traced on the faces which correspond with those of the 
rhomboidal parallelopiped,) form angles of 6 o° and 120°. It 
would therefore be an error to consider them as indications of 
the form of the elements of crystallization, as we are tempted 
to do from a simple inspection of the crystal. These same lines 
