244 Count ae Bournon's Description of 
blue ; and the stone which possesses this colour is distinguished 
by the name of sapphire. The yellow colour is seldom pure, 
being in general more or less mixed with a reddish tint. The 
oriental gem of this colour is called the oriental topaz. From 
a duly proportioned mixture of the blue and the red, is pro- 
duced the purple colour, which constitutes the oriental amethyst. 
Sometimes the red colour is predominant, at other times the 
blue; and, in the latter case, the stone possesses that beautiful 
purple colour which is so pleasing to the eye. Stones of this 
colour are among the most rare of those belonging to this 
substance. By the union of the blue colour with the yellow, 
is formed the green, which produces the oriental emerald ; but 
there is usually mixed with this colour a small proportion of 
red, which gives to the green a brown and rather dull tinge. 
Sometimes however the yellow colour is predominant, which of 
course gives the green a yellowish cast, and then the stone 
becomes the oriental chrysolite. I have not yet seen any of the 
green stones, or oriental emeralds, in which the green colour 
was perfectly pure and brilliant, as it appears in the true emerald, 
called the peruvian one. In the mixtures of which I have just 
spoken, the colours are, in general, perfectly blended together; 
sometimes however they exist in a separate state, and so dis- 
tinctly, in the same stone, that the mixed colour is only per- 
ceptible at the point where the different colours meet. At other 
times, these colours being only coarsely mixed, and not blended 
together, the stone presents the one or the other of them more 
distinctly, according to the position in which it is held. 
TRANSPARENCY. 
The crystals of corundum from the Carnatic, having their 
