green, yellow, or blue, and is used in Germany for cheap
jewelry.
The opal was prized by the ancients above most other
precious stones. The Romans obtained their supply from the
East, perhaps from Ceylon, where they are now found, but
the largest did not exceed the size of half a hazel-nut, except
the famous opal of Nonius, who preferred exile rather than
surrender it to Mark Antony. This historical gem has been
variously priced from one hundred thousand to nearly one
million dollars,— quite a difference to reconcile, but it proves
the high esteem in which the opal was held at that time.
This gem is very difficult to engrave, and sometimes quite
impossible, yet there are a few antique works of the kind,
including one belonging to the Orleans collection, and another
in Paris engraved with the portrait of Louis XIII. Some
rude intagli, apparently antique, are occasionally found in this
stone, usually of the opaque varieties. There is a fine specimen in the Praun collection, engraved with the heads of
Jupiter, Apollo, and Diana.
On account of its softness, frangibility, and liability to injury
from oily substances, it is not suitable for ring-stones, but may
be used, with proper care, for other ornaments. Unfortunately, this desirable gem is affected by atmospheric influences,
as severe cold, which, it is thought, causes exterior flaws
tending to extinguish all its " fire," and reduce it to a common
pebble. The only essential remedy for this defect is to remove
the outer layer, but this operation is open to objections since
it diminishes the thickness of the stone, and allows a freer
passage for the light through it, and, as a result, its beautiful
iridescence is impaired or lost.
The opal was counterfeited more successfully by the
ancients than any other gem, so that it was nearly impossible,
