MR. J. T. HOTBLACK ON PRECIOUS STONES. 
29 
the old jewellery of local families. It is said that good stones 
are now seldom found. 
The amethyst also was once much more valuable than now. 
I have seen it stated that so recently as 1867 a good coloured 
amethyst, of the size of a 2s. piece, was worth £10 or £15, and 
that in 1652 an amethyst was worth as much as a diamond of 
the same size. 
Now, rock crystals of all colours have been found in Brazil in 
such immense quantities that they have very much sunk in value, 
and it is even said that many of the Scotch cairngorms are really 
Brazilian stones. 
Chalcedony 
is the same material as rock crystal, but not crystallized, and 
slightly less pure. Its hardness and S.G. are almost exactly the 
same. When dark red it is sard, when lighter red it is 
carnelian, when yellow to white it is carnelian, when striped 
it is agate, when black or dark brown with white layers it is 
onyx, when red or light brown with white layers it is sardonyx, 
when chatoyant it is a cat’s-eye. 
This is the stone in which the beautiful cameos of the ancients 
were almost exclusively carved, and it is still used for that recently 
revived art. It has been esteemed from the earliest times as 
superior to all other stones for the engraving of seals, and it is still 
almost, if not quite exclusively, used for that purpose. It is also 
used to-day in enormous quantities for all sorts of cheap jewellery. 
Jasper, which may be any colour, and bloodstone, which should 
be green with red spots, are closely allied to chalcedony, but are 
slightly less pure. The latter is used principally for ring-stones, 
the former, more for decorative cabinet-making and building purposes 
than for jewellery. 
Opal. 
Another uncrystallized form of silica is, perhaps, nearer to rock 
crystal than chalcedony, being almost pure silica with a little water, 
varying from 6 to 10 per cent., but the hardness is less from 5.5 to 
6.5, and the S.G. 2.0 to 2.3. Every one knows this beautiful gem. 
When in perfection it is the noble or precious opal, and is very 
