20 
MR. J. T. HOTBLACK ON PRECIOUS STONES. 
America, i.e., in the States, weighing five tons, and still said to be 
crystal, and not amorphous. When white, or indeed of any 
common colour, it is often mistaken for quartz crystal ; but the 
crystals are seldom perfect, or of a uniform colour, and so good 
emeralds, even of a moderate size, are of considerable value, for the 
same reason this stone is almost always cut table-topped. 
Zircon. 
The stone I propose to put next is properly called zircon, but 
more generally according to its colour, hyacinth or jacinth ; it is 
7.5 in the scale of hardness, its S.G. 4.0 to 4.75, and its 
composition is about 65.0 zircon and 33.0 silica. The various 
shades of red, including orange red and poppy red, are called 
hyacinth ; brownish yellow, reddish brown, and cinnamon are 
jacinth ; if green, yellow, brown, white, and grey it is called 
jargoon, and sometimes the white stones are called Matura 
diamonds. 
This stone is seldom used in jewellery in its own name, but is 
frequently sold as diamond, it being more like a diamond in lustre 
than any other substitute ; not long since jargoon was supposed to 
he inferior diamond. It is found in very many places, including 
Vesuvius, in ejected blocks, the Island of Harris in the Hebrides, 
and in Ireland, but, perhaps, in greatest abundance in Matura in 
Ceylon, and is called by the natives Matura diamond, except to 
the uninitiated when the Matura is omitted. It is seldom found 
of a larger size than 10 carats. Its value in the rough is nominal 
and I can only wonder that a stone with so much beauty is not 
more used than it is. 
Zircons, in every way identical with the zircons of nature, are 
said to have been produced artificially to M. Henri Deville by 
passing fluoride of silicum over zircon at a red heat. He, therefore, 
believes that zircon has been formed by igneous agency. 
Tourmaline. 
The next stone I shall treat of is the tourmaline, from 7.0 to 7.5 
in the scale of hardness. The composition varies considerably, but 
there is always nearly 40.0 of silica, from 30.0 to 40.0 of alumina, 
and from 5.0 to 8.0 of boracic acid; in addition there is sometimes 
about 14.0 of magnesia, but in specimens from Siberia there is 
no magnesia; and in the green from Brazil, there is about 6.0 of 
