A SYSTEM OF 
SECT. LV. 
I. The Opal. Opalus P^derota, 
It is the moft beautiful of all the flint 
kind, owing to the changeable appearance 
' of its colours by refledion and refradion, 
and muft therefore be defcribed under both 
thefe circumflances. 
The Opal of Nonnius, the Sangenon of 
the Indians. 
This appears olive-coloured by reflec- 
tion, and feems then to be opaque, but 
when held againfl: the light, is found 
tranfparent, and of a fine ruby red. 
That opal is fuppofed to have been of 
this kind, which Pliny mentions in his 
Natural Hiftory, chap. 307. fed. xxi and 
which he fays, was in the fenator No- 
nius’s pofieffion, who rather fuffered ba- 
nijfhment, than part with it to Antony. 
This ftone was in Rome at that time 
valued at 20000 fefterces. But the ftone 
here particularly defcribed, was found in 
the ruins of Alexandria ; it is about the 
fize of a hazie-nut, and was bought for 
a trifle of a French druggift, named 
Roboly, and prefented to the French ge- 
neral conful Lironcotirt, who afterv/ards 
offered it to fale in feveral places, for the 
fum of 40,000 rixdollars. See Haflel- 
quift’s Travels td the Eaft, under the ar- 
ticle of Opal. ^ 
* This very ftone was in the year 1763 in the poftellion 
of his excellency the duke de Nivernois, then ambaftador to 
the Britifli court, and I have often been honoured by his ex- 
cellency of having it for fome days in my pofteftion. D. C. 
There 
