properties.
Dr. Manuel Gutierrez says of these that on the hills of the El
Astillero estate, which is in the jurisdiction of Contepec, and in the
State of Michoacan, were discovered some very rich beds of opals, but
D. Jose Maria Siurob of Queretaro, the owner of the Esperanza mines,
his informant, did not give him more definite particulars.
At
present (1889) only one mine is being worked by the owner of six of the
largest mines. The rock containing opal is brought to the city of
Queretaro, a distance of twenty-five leagues, and about twenty
lapidaries are continually employed in cutting and polishing the stone.
The miners receive an average of twenty-five cents a day and the
polishers an average of seventy-three cents for their work.
The
noble opals found in Mexico generally exist (unfortunately) only in
thin layers, between or upon layers of common opal, without any play of
fire. Often only one-half or two-thirds of the cavity which contains
this variety is filled with opal, and it generally shows stratified
layers, like an onyx. A layer of hyalite is often present on the upper
layer, or else the opal is very smooth, the opal coating being thin,
with a very strong play of color, usually too thin to be polished. Both
of these varieties of opal exist in great abundance in Mexico, and many
thousand stones are sent to Germany to be remounted in the cheaper
class of jewelry. Thousands are annually sold to visitors to the cities
of Mexico, Queretaro, and at railroad stations in Mexico, and in Texas,
New Mexico, and Arizona in the United States.
The
fire-opal is perhaps the most gorgeous of all varieties of the opal,
and it is also the most sensitive. It is frequently injured by water
or exposure or by sudden atmospheric changes; indeed, so easily
affected are fire-opals by the vicissitudes of the weather that they
are believed to be brighter in summer than in winter, though this
difference may be due to the fact that the light is better and the
weather is warmer in summer. Some varieties are not so easily
influenced, however, and are not injured by contact with water. Stones
have been known to lose their brilliancy even when removed from the
influence of atmospheric changes; when wrapped in paper, and placed in
a jeweler's iron safe, or in the drawers of a collector's cabinet, they
have lost
