~bS Count de Bournon's Description of 
corundum but likewise of the perfect kind, of all colours, ano- 
ther accidental variety, which is particularly met with when their 
irregularity and their opacity announce a want of perfection in 
their crystallization. Sometimes the edges of the crystalline 
laminae may be perceived upon their terminal faces ; and, there 
being more or less distance between them, they exhibit very 
much the appearance of an irregularity, or a kind of disturbance, 
in those laminae which seem to have been deposited upon these 
faces, and in a direction parallel to them. But, with a little 
attention, we may perceive that these laminae, the edges of which 
are in the direction of three of the alternate solid angles of this 
extremity of the crystal, can only belong to the laminae depo- 
sited upon the faces of the primitive rhomboid ; and, we are very 
often able, at the same time, to discover their degree of incli- 
nation. 
A third circumstance attending these crystals, and one which 
it is more difficult to explain, consists in the appearance of con- 
centric hexagons, parallel to the hexagon formed by the exterior 
edges of the crystal. These hexagons may sometimes be ob- 
served upon the terminal faces, as is shewn in Fig. 35. Their 
edges have a degree of thickness very perceptible by the eye ; 
and may besides be frequently distinguished from each other, 
by a difference in their transparency, and sometimes also by 
a greater or less intensity in their colour. There are preserved, 
in Mr. Greville’s collection, amongst a pretty large number 
of crystals in which this circumstance has taken place, two 
crystals of imperfect corundum from the coast of Malabar, that 
exhibit it in a very striking manner. In the first of them, one 
only of these hexagons, placed at nearly an equal distance 
from the centre and the edges of the terminal face, is of a blue 
