goo Count de Bournon’s Description of 
the crystals approaching nearer to each other, and diminish- 
ing in size, so as at last to become invisible: very often, they 
shew themselves only in the form of small filaments, scarcely 
perceptible. 
The above is not the only substance which presents the phe- 
nomena just described, even in the stones here treated of ; 
the thallite sometimes has the same appearances ; and, in that 
case, it gives to the matrix a green colour, similar to its own. 
When this happens, we may sometimes, by means of a lens, 
perceive small microscopic crystals of thallite ; very often, how- 
ever, they are too small to be distinguished. 
It appears therefore that coloured stony substances, by inter- 
posing themselves, in particles too small to be seen, in stones, 
may sometimes produce the same effects (and probably in the 
same manner) as are produced by the various metallic oxides. 
Very attractable black Oxide of Iron. This ore of iron (which 
is the fer oxidule of the Abbe Hauy, and the magnetic iron ore 
of the Germans,) is also found sometimes in the matrix of im- 
perfect corundum from the peninsula of India; but, as we shall 
hereafter see, it is by no means so general, nor so abundant, in 
that matrix, as it is in the matrix of imperfect corundum from 
China. In the former, it appears in small grains of an indeter- 
minate shape, which are sometimes interposed between the 
particles of hornblende, in such a way as might easily lead us 
to suppose, that the latter substance has the propert}^ of being 
acted upon by the magnet. In those parts of the matrix which 
contain this oxide of iron, are found hexaedral prisms of corun- 
dum, the surface of which is entirely covered by a layer of the 
oxide, about a quarter of an inch in thickness, and absolutely 
moulded upon them. 
