Further
information about these interesting and often beautiful forms of silica
will be found in Mr. Eudler's article on " Agates and Agate Cutting" {Popular Science Review, Vol.
I.); and in the article on " Agates, Carnelians, and Jaspers " ("
Trans. Scot. Nat. Hist. Society," Vol. I.) ; and the "Guide to the
Collection of Scottish Agates" (H.M. Stationery Office), both by the
late J. G. Goodchild, of H.M. Geological Survey.
212. Opal.
Opal
is a mineral of very similar composition to Quartz, yet its whole
character differs from that of Quartz in a marked way. It was known in
ancient times, and Pliny gives as good (and as often quoted) a
description of it as can be worded. The great value set by the Romans
on the gem may be gathered from Pliny's account of the Opal belonging
to Nonius, who was proscribed in the hopes of making him give up his
gem to the Triumvir. Bather than do this he fled. His gem was valued at
what would now be £20,000, and yet it was no larger than a hazel-nut
(King).
It
is a stone that has always been surrounded in the popular mind with a
mass of superstitions. In early times it was held to be a protection to
the sight. This seemingly led Marbodus to alter the name of it to
Ophthalmius, and at the same time to endow it with the further virtue
of rendering the wearer invisible. Thus at this time it was rather a "
lucky " stone. Now it remains as one of the few stones to which one
hears superstitions attached; but its property has mysteriously
changed, and it is not unknown to hear " Oh! I never wear Opals, they
are so unlucky."
