50 AVANTURINE CATS -EYE. 
price of inferior seal-stones varies from ten shillings to 
three or four pounds each ; but those of superior beauty 
will produce from five to ten guineas. Such specimens 
as have a pure and full yellow colour are often sold 
for topazes. When they are muddy, the lapidaries have 
the art of entirely dissipating the colour, and giving 
them a transparent lustre. This is done by means of 
heat, which will dissipate the colour of every species 
of crystal. 
85. AVANTURINE is a quartz, generally of reddish 
colour, sprinkled with yellowish shining points of mica (123), 
which are dispersed through its whole substance. 
A French artist, some years ago, having by accident, 
or " par aventure," suffered a quantity of brass filings 
to fall into a vessel of melted glass, afterwards found 
that it was admirably calculated for vases and different 
kinds of ornamental work. Hence he denominated it 
avanturine, a name which mineralogists have since ap- 
plied to those natural objects of which this production 
of art was an apparent imitation. 
Avanturine is found in some of the countries border- 
ing upon the White Sea, in Spain, and some parts of 
France. In the late Leverian Museum there was a 
piece which weighed near five pounds, and was unique 
both for beauty and magnitude. It had been disco- 
vered in 1788, amongst the ruins of the triumphal arch 
of Julius Csesar in the valley of Suse, in Piedmont; and 
was purchased of the person who found it for 200 
guineas. Avanturine is cut into various ornamental 
articles, which are sometimes sold at a very high 
price. 
Imitations of it are very common, and are formed by 
the simple operation of throwing brass or copper filings 
into coloured glass in a state of fusion. 
86. CATS-EYE is a stone of brownish grey colour, tinged 
with green, yellow, white, or red; semi-transparent, and re- 
flecting from its interior a splendid white line or speck, which 
