448 Mr. Greville on the Corundum Stone , &c. 
The mark * distinguishes the specimens in my collection, to 
which I have referred in the foregoing Paper. 
The mark -f distinguishes the stones which, from their 
specific gravity, I think belong to the genus of Corundum. 
The generic name Corundum, I am in the habit of giving 
to those sorts which have a sparry or a granulated fracture. 
When Corundum has a vitreous cross fracture, I call it sap- 
phire ; and distinguish its varieties by their colours, white, red, 
blue, yellow, green ; and by the accidental reflection of light 
from their laminae : when in one direction, I call the sap- 
phire chatoyant ; when the reflection is compounded of rays 
which intersect each other, and appear to diverge from a com- 
mon centre, I call them star-stones, as red, blue, or greyish 
star-stones, or star-sapphires. 
