118 A Book of Precious Stones
stones are found in many lands. Mines in Czernowitza,
in northern Hungary, long produced the most highly valued gem opals
obtainable. These opals are often known as " Oriental opals," because
they first appeared in Holland through Greek and Turkish traders.
Despite the trade practice of applying the term " Oriental " to this
type of opals, none is found in the Orient. The Hungarian opals were
undoubtedly those first known to the Romans. The claim is made that
Hungarian opals are less likely to deteriorate than any other variety.
Gem opals are also found in Australia, Mexico, and Honduras. Although
opals are produced to a commercial extent in several Mexican states,
they are most systematically mined in Queretaro, where the opal occurs
in long veins in a porphyritic trachyte. This opal mining has created a
somewhat primitive cutting and polishing industry in the city of
Queretaro. The exporting of Honduras opals—all uncut—is not extensive.
In the United States the occurrence of gem opal has been observed in
the John Davies River, Oregon, and near Whelan, between the Coeur
d'Alene and Nez Perces Indian reservations, almost on the Idaho line,
State of Washington. The most prolific source of opals
