The
opal has no colour that may be called its own, but a faint bluish tinge
analogous to the tint of certain resinous quartz, of which it is a
variety.
Its
true beauty and its great value are produced by a physical accident; it
is traversed by a multitude of fissures filled with air and moisture,
which reflect all the prismatic colours. The tender violet of the
amethyst, the blue of the sapphire, the green of the emerald, the
golden yellow of the topaz, and the flashing red of the ruby, appear at
times isolated in certain parts of the stone, at times crossing each
other in vivid play with an effect that is magical.
The opal is found in Arabia, Ceylon, Hungary, Saxony, Ireland, Iceland, Scotland, and Mexico.
Hungary
and Mexico furnish the greater number to commerce; and some beautiful
specimens have been recently brought from Honduras. The stones from all
these places are true opals. Connoisseurs can usually distinguish the
precise locality from which they are derived at a glance.
The
opal occurs in veins or gangues in ancient formations, and is not
scarce; but the parts that, after cutting, will display all the storied
fire of the opal are very rare.
Beginning
at the resinite quartz without fissures, and consequently without fire,
and choosing successively fragments more and more closely fissured
until the maximum is reached of the effect of light,
