variety
exhibiting a delicate play of colors, and is obtained from Hungary,
Australia and Mexico. The Fire Opal, much less valuable, is translucent
and red or reddish-yellow in color, and found almost exclusively in
Mexico.
Opalized Wood: Wood
that has been changed into Opal in such a manner as to retain its woody
structure. It is often cut and polished for use as an ornamental stone.
The principal sources of commercially valuable opal material in the
United States are the opalized forests in Apache County, Arizona, Napa
County, California and at Virginia City, Nevada.
Orpiment: Yellow
Sulphide of Arsenic. Sulphur 39%, Arsenic 61 %. This mineral occurs
usually in foliated or columnar masses, and in small rarely distinct
crystals, in several shades of lemon-yellow. Its name is from the
Latin, signifying "yellow paint," or "golden paint." It occurs in the
same forms and in the same places as Realgar, the red sulphide of
arsenic, and is a nonconductor of electricity.
Native
Orpiment, mixed with water and slaked with lime, is used in the East as
a wash for removing hair; it is employed as a pigment in dyeing and in
calico printing.
In the United States it occurs at Edenville, N. Y., and in the deposits of Steamboat Springs, Nevada.
Orthoclase: Silicate
of Aluminium and Potassium. Silica 64.7%, Alumina 18.4%, Potash 16.9%.
It occurs in crystals, often massive, sometimes compact and
flint-like, is colorless, white, yellow, and flesh-red; rarely green.
Adularia is a nearly pure, nearly transparent variety of Orthoclase,
and Moonstone is a translucent Adularia, with a pearly luster and
slight play of colors. Sunstone is a translucent reddish variety.
Orthoclase occurs in Silesia, Prussia, the Tyrol, the Alps, Italy, and many places in the United States.
This
mineral is much used in the manufacture of porcelains and china, both
as constituents in the body of the ware and also to produce the glaze.
Ouvarovite Calcium Chromium Garnet. Emerald-green variety or Uvarovite: of
garnet. Green garnets are rare, occurring only with chromite in
serpentine, in the Ural Mountains, and in the chromite mines of Texas,
Pennsylvania, California. The purely transparent specimens are
beautiful, and are used as gem stones.
