"The
opal, when pure and uncut in its native rock, presents the most lovely
colors seen in the world, except those of clouds," says Ruskin, in his
lecture on "Color." The mineral composing the opal does not, however,
always show the brilliancy of colors which we usually associate with
the gem. Chemically, it is an oxide of silica, and is therefore much
similar to quartz. As a mineral, opal is quite common, and one of its
interesting occurrences is in the Yellowstone Park, where the geyser
and hot spring formations are composed almost entirely of this
silicate known here as geyserite. It may be said, therefore,
that the waters of the park build up cones of opal and fall into opal
basins. In the rarer form in which it displays its many fascinating
colors the gem is of comparatively rare occurrence. The most noted and
most ancient mines are those of Czernowitza, in northern Hungary. It is
well established that the Romans obtained their opals from these mines.
At the present day, however, this ancient source has become
