the Corundum Stone , and its Varieties, &c. 285 
alteration or decomposition of the stone, had afterwards com- 
bined with a portion of carbonic acid. 
To the above mentioned lime, (carried away by the rains 
which wash the exposed parts of the rocks composed of this 
substance, and deposited upon the fragments of corundum scat- 
tered at the feet of those rocks,) ought no doubt to be attributed, 
that calcareous incrustation which is frequently observed to 
cover, either partially or entirely, many fragments of imperfect 
corundum, found among the specimens of that substance sent 
to us from India. 
If we let a piece of this matrix remain for a certain time in 
nitric acid, it is attacked by it, without being dissolved, and 
without changing its form; but if, after being taken out, it is 
pressed between the fingers, it may be crumbled by a very 
trifling effort, and may, by being rubbed, be reduced to a sort 
of paste. 
SUBSTANCES WHICH ACCOMPANY THE IMPERFECT CORUNDUM, IN 
THE ABOVE MENTIONED MATRIX, FROM THE PENINSULA OF 
INDIA. 
Felspar . There are sometimes found, in the matrix here 
treated of, pieces, more or less considerable in size, of a lami- 
nated substance, which has the same greenish gray colour, the 
same brilliancy, and, in short, the same appearance, in many 
respects, as the corundum itself. It is indeed the more easy to 
confound this substance with corundum, as it is frequently ac- 
companied with crystals of the latter. I have myself been several 
times led into this mistake, before I had paid such particular 
MDCCCIT, P p 
