2^4? Count de Bournon’s Description of 
in consequence of which, the pieces, when taken out of the acid, 
may be easily crumbled by the slightest pressure of the fingers ; 
and nothing remains in its former state, except the small par- 
ticles of the thallite. 
There exist some pieces, in which the particles of the matrix 
are infinitely more numerous than those of the thallite itself; 
the latter then only appears in the form of small greenish or 
yellowish points, disseminated in greater or less proportion, and 
in detached spots. 
In the second of the states in which this substance is found 
in the matrix of corundum, it appears in the form of pretty thick 
prisms ; these prisms have deep grooves or channels, which, as; 
is often observed in the crystals of tourmalin, render their shape 
absolutely deformed. The substance, in this second state, is 
more pure; no particles of the matrix, which were said to be 
mixed with it in its first described state, are to be seen. The 
semi-transparency is more general, and in a greater degree. 
The green or yellowish colour is also more deep; and sometimes 
a slight tinge of red is mixed with those colours. Some parts 
of the pieces are less grooved than others ; and those parts in- 
dicate the forementioned rhomboidal prismatic form of 128° 30*" 
and 51° 30' ; but it is very difficult to obtain an even fracture of 
this stone. 
In the third state, this substance is so very similar to the 
purest imperfect corundum, that at first I supposed it to be of 
the same nature ; and it was not until I had examined it more 
particularly, that its specific gravity and its hardness, so dif- 
ferent from those of corundum, led me to think it could not 
possibly belong to that substance, and that it ought, from those 
characters, to be ranged with the thallite. The analysis of 
