18 
MR. J. T. HOTBLACK ON PRECIOUS STONES. 
water 3.0. The S.G of diamond being 3.4 to 3.6 and its composi- 
tion pure carbon. 
This stone, when green, is the Oriental emerald, one of the 
rarest and most beautiful of all gems. Emanuel says in his work 
on precious stones : “ I have only met with one specimen.” 
When yellow the Oriental topaz. Oriental amethyst, aquamarine, 
hyacinth, peridot, chrysolite, &c., are all corundums, the colour of 
the gems after which they are called, but to which they are very 
superior. 
White and yellow corundums are constantly being sold as 
diamonds. The King of Portugal, I think, is said to have the 
largest diamond in the world, if it is not a -white sapphire. The 
ruby should be the colour of pigeon’s blood, when it is much more 
valuable than the finest white diamond. 
From the earliest middle ages a ring set with a sapphire and 
worn on the fore-finger has been the symbol of investiture with 
the office of bishop, by reason of its violet colour agreeing with the 
Episcopal vestments. See King’s antique gems. These rings are 
well known to most antiquarians, there are several in the Fitch 
Collection in the Museum, and I have one found locally not 
long since. 
As the diamond is pure carbon, so the corundum is nearly pure 
alumina. 
Chrysoberyl. 
The three following stones decrease in hardness in proportion as 
they have less alumina in their composition; the hardest of them, 
and the next hardest to corundum, is the chrysoberyl, it has about 
80.0 of alumina, and almost all the rest glucina, and is reckoned 
8.5 in the scale of hardness, and the S.G. 3.4 to 3.8. This stone 
is of comparatively little value, except when opalescent as a cat’s 
eye, when it is called a chrysoberyl cat’s eye, or if milky opalescent 
a cymophane cat’s eye, both of which are very valuable, epecially if 
the rays are brilliant. Yet the white chrysoberyl, when cut as 
a brilliant, has considerable lustre, and is easily mistaken for 
a diamond. The yellow, greenish yellow, brownish yellow, and 
reddish brown are called chrysolite, the reddish green is 
Alexandrite. The refraction of this stone is double in a high 
degree, which makes it very difficult to cut properly, and this is, 
I think, the reason for its little use. 
