the Corundum Stone, and its Varieties, &c. 247 
perfect. To the same cause must also be ascribed, the scarcity of 
fragments of sapphires, in comparison with those of rubies, in 
the sand of Ceylon which has passed through the hands of the 
lapidaries; the fragments of the former being usually more 
transparent, they are selected from it, as more worthy to be cut 
and polished. 
HARDNESS. 
Corundum is, next to the diamond, the hardest of all stones ; 
but, with respect to this character, the degrees of intensity are 
various ; and this variety depends principally upon the degree 
of purity, and the colour, of the stone. 
When the imperfect corundum of the Carnatic is neither of 
a blue nor of a red colour, its hardness is less considerable, in 
proportion as its transparency is less, and its internal substance 
more full of those lines or fissures, which, as I have already 
said, are commonly observed in it. Such corundum may be 
scratched by that which is more transparent, though of the same 
colour. The latter, (supposing the degree of purity to be nearly 
equal, ) may in its turn be scratched by that which is of a purplish 
red ; and this last, by the corundum of a blue colour ; which is 
the hardest of all those varieties of this stone that I have dis- 
tinguished by the name of imperfect corundum. The hardness 
of the imperfect corundum of China, and of that from the coast 
of Malabar, appear to be equal. This hardness, which is rather 
inferior to that of the blue corundum of the Carnatic, is how- 
ever somewhat greater than that of the other varieties. 
The perfect corundum of Ceylon of a red colour, or oriental 
ruby, the hardness of which seems to be nearly the same as 
that of the imperfect blue corundum, is superior in hardness 
K k 2 
