the Corundum Stone, and its Varieties, &c. 2% 
colour, while all the rest of this face is gray, slightly tinged 
with red, and chatoyant. (Fig. 36.) In the other, the last 
concentric hexagon alone, or that which at the same time 
forms the exterior part of the crystal, is (for the thickness of 
about half a line) of a blackish-brown colour, dull and opaque ; 
while the rest of the terminal face (which likewise exhibits 
concentric hexagons) is of a gray colour, but has a silvery 
hue, because this part of the stone is chatoyant. (Fig. 37.) 
The above circumstance seems to announce a deposition of 
laminae upon the sides of the hexaedral prism ; nevertheless, 
if we attempt to break these crystals according to that direc- 
tion, we find that it is absolutely impossible to succeed, in such 
a way as to obtain a fracture that has the appearance of being 
made in the natural joints of the stone ; whereas, on the con- 
trary, fractures may be made with sufficient ease, in a direc- 
tion corresponding to the faces of the primitive rhomboid. 
Notwithstanding these concentric hexagons, there may be some- 
times perceived, upon the same terminal faces of the prism, traces 
of the edges of the laminae already mentioned ; and the crystal 
then exhibits the appearance represented in Fig. 38. As the real 
direction of the laminae (which is shown in these crystals by 
their natural fractures) indicates that the rhomboid of g 6 ° and 
84° is the primitive form of this substance, it seems necessarily 
to exclude the other direction, of the existence of which (as we 
have seen) there is some appearance, and which would give the 
hexaedral prism, as the form of the primitive crystal. 
The above appearance, however, is certainly owing to a parti- 
cular cause; but it seems' to me, that the laws hitherto established 
in crystallography, are by no means capable of furnishing one 
that can account for it in a satisfactory manner. The only 
mdcccii. ! N n 
