2% Count de Bournon’s Description of 
FRACTURE AND TEXTURE. 
I have already observed, that all the stones which compose 
the various kinds of this substance, to which I have given the 
general name of corundum, have a lamellated texture, in a 
direction parallel to the faces of a rhomboid of and 84° ; and 
also, that they break in a direction parallel to the said faces. 
The blue variety of perfect corundum, or sapphire, follows 
the above law, as well as all the other varieties. It is true, 
however, as I have already had occasion to mention, that the 
ease with which the crystals of this substance may be divided, 
is very various ; but observation shows, at the same time, that 
these variations are governed, in the first place, by the degree 
of force existing in the attraction of the molecules which com- 
pose the crystals, as well as by the perfect adhesion of the 
crystalline lamina? (composed of these molecules) at all points 
of their surface; two facts, the existence of which is shown 
by the difference in the degrees of hardness and transparency of 
this stone, and which appears to be very considerable. In the 
second place, the variations here spoken of seem also to depend 
very much upon the colour these stones possess ; for, as I have 
already observed, they must be governed by the force of 
attraction, which, in my opinion, varies with the colour. This 
force appears to exist in the highest degree, in the perfect co- 
rundum of a blue colour, or sapphire ; it being with great diffi- 
culty that this kind of corundum can be broken, in the direction 
of its laminae, in such a manner that its fracture shall present 
that even surface, and that kind of gloss, which fractures made 
in the above direction generally exhibit. It may be broken with 
equal ease in any other direction ; for instance, in a direction 
