28 
MR. J. T. HOTBLACK ON PRECIOUS STONES. 
Merchant’ was on my passport.” I have also found it, as have 
others, in the “forest-bed.” Amber is not much esteemed for 
jewellery in this country, but in Turkey and neighbouring Asia it 
is a good deal thought of. 
Jet 
is really a variety of coal, with a hardness of only 1.5, and a S.G. 
of 1.3. It is much blacker, tougher, and harder than ordinary 
cannel coal, and is capable of taking a very bright polish. It was 
at one time much used in England for mourning jewellery. It is 
found in detached pieces in clay at Whitby and other places in 
Yorkshire, also on the Baltic Coast, in the Ardennes, and the 
Pyrenees, but some of the very best is dredged by the fishing-boats 
in the North Sea, and sold at the fishing ports to the same dealers 
as buy the amber, but at a much lower price. Jet is still much 
esteemed in Spain, and also in Turkey. Jet is but slightly heavier 
than water ; it burns readily, and emits a strong, sweet bituminous 
smell. 
Bock Crystal. 
This, with the uncrystallized forms of the same material (i.e., 
silica), is so important, that instead of putting them in their proper 
places, according to their hardness, I have preferred to treat of 
them last of all, for as the diamond, which is pure carbon, heads 
the list of stones, so I think rock crystal, chalcedony, and opal, the 
first of which is practically pure, and the others almost pure silica, 
may very properly end the list of precious stones, both by reason 
of their great abundance and their very general use. 
Rock crystal is about 7 in the scale of hardness, its S.G. is 2.6, 
and it is practically pure silica. It is very largely used in jewellery 
under various names. When white it is sometimes called by its 
proper name, at others it is Cornish or Bristol diamond, when 
violet it is the true amethyst, when yellow or brown the cairngorm, 
when red rose quartz, and I more than suspect that most of the 
topaz is but pale yellow rock crystal. Jewellers, when they wish 
to be precise, call it false topaz, and much aquamarine is but the 
same stone, sea-green. Unfortunately rock crystal can be easily 
artificially coloured. At one time Cornish diamonds were highly 
esteemed, and some finely-cut examples are still to be met with in 
