The Opal
	"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