Opal is brittle, heat sensitive, and breaks and scratches easily;
additionally, some varieties self destruct through the loss of water. Even with these drawbacks,
opal's unsurpassed beauty guarantees its status as a premier gemstone. The derivation of
its name even adds to its position.
Reportedly, opal's name evolved from the Roman word opalus from the
Greek word opallios meaning "to see a change of color." The Greek word was a modification
of the ancient Indian Sanskrit name for opal, upala, which meant "precious stone."
If one spoke in mixed tongues, then opal would be opallios upala, "to see a change
of color precious stone." As indicated by the derivation of its name, opal has centuries
of history as a treasured gemstone.
Historically, beliefs associated with the wearing of opal have varied.
The early Greeks thought that opals gave their owners the powers of foresight and prophecy,
and the Romans adored it as a token of hope and purity.
regarded it as sacred, and Arabs believed it fell from heaven. In the nineteenth century, superstitions grew about the bad luck or fate that could befall one for wearing opal if it were not the
Today, these superstitions have diminished, but some people still believe
it is bad luck to wear opals. We have also heard people who try to fool themselves, by
beleving It's "OK" if the opal is given as a gift.
has over one hundred variety and trade names, but the list of accepted
or commonly used names is much shorter.
The most important and most widely known opal is the precious opal.
Precious opal may be subdivided further by color modifiers, white, black,
pinks, and blue, which describe the body color of the opal. Australia
is famous for its white and black precious opal.
Fire opal, the bright red, reddish-yellow, orange, or brownish-red
body colored opal is the second most important opal commercially. Until
recently, the best fire opal came from Mexico. Arizona.--Two commercial mining operations in Arizona produce
blue precious opal. The body color is a light or pale blue with strong play of color
in red, blue, green, and orange. The two operations sell most of its material as finished stones
at the Tucson Gem and Mineral show and other local gem shows.
Idaho.--In Idaho, opal is the second largest contributor to the total
value of gem material produced. The varieties produced include precious
(white and pink), yellow, blue, pink, and common. The Spencer opal mine,
the largest privately owned gem stone producer in the State, is the major producer of opal. At Spencer the precious opal occurs
as one or more thin layers within common opal partially filling gas cavities within a
rhyolite-obsidian flow. About 10% of the material is thick enough to cut into solid gems; the
remainder is fashioned into doublets and triplets. The Spencer Mine is
the source of pink common opal and pink precious opal.
Louisiana.--The reported precious opal from Louisiana is a sandstone/quartzite
with precious opal cement and matrix. It has blue or purple play of color.
The material could be cut into cabochons for jewelry and other items of
interest. To date, most of the material has been cut into large (over
2-inches in diameter) gemstone spheres.
Nevada is known for precious opal from Virgin Valley. The first discovery
of precious opal in the Virgin Valley area was in 1905 or 1906. Since then a significant
quantity of the highly prized opal has been recovered. Virgin Valley opal
is comparable to any in the world for its vivid play of color and in terms of the size of material available. Individual
pieces weighing over 3 kilograms have been recovered from the Virgin Valley deposits.
In 1993, miners found a 100-kilogram opalized log containing precious opal. The material
varies in body color from deep pure black to brown to yellowish-white to white to colorless.
The play of color includes all colors common to precious opal, red, blue, green, yellow,
orange, etc. The opal occurs primarily as replacement of wood, or sometimes, as replacement
of conifer cones. Some opal does occur as nodules filling void spaces in clay. The
wood replacement is so complete, that generally the wood grain and banding are no longer
visible. The exception to this would be that often the exterior wood texture is
still present as a brown or black rind. The uses of the opal can be restricted because of
crazing. Crazing is the breakdown or deterioration of opal by the development of very fine
cracks all over the surface that extend until they intersect. In the worst
cases, the surface of the opal deteriorates into a crumbling sand-like material. Because of the crazing
the opal is not well suited for use in jewelry, but displayed in water, glycerine, mineral
oil or other liquids makes remarkably beautiful mineral specimens. The
mineral collections of most of the better museums contain very fine pieces of Virgin Valley opal. Many museum
pieces are crazed from exposure to the air. During the summer months, at least two
dig for fee mines in Virgin Valley are open to individuals. One mine is operated by the
Hodson family and the other by the Wilson family. Individuals pay a daily
fee to dig and keep all the opal that they find. Other mines in the area
are commercial opal producers. Two other locations in Nevada also have
produced precious opal. The opal does not have as good a play of color
as that from Virgin Valley and it has the same crazing problem. One location is
south of the Virgin Valley in the Calico Mountains of Humboldt County,
and the other is near Gabbs in Nye County. The three precious opal locations
and many other locations around the State produce common opal and opalized wood.
Oregon.--During 1988, West Coast Gemstones, Inc., began mining and marketing
a variety of very fine-quality opals from Opal Butte in Morrow County, OR. The varieties
produced includes hyalite, rainbow, contra luz, hydrophane, crystal, fire,
blue, and dendritic. Exquisite stones as large as 315 carats have been
cut from contra luz rough from this deposit. The deposit at Opal Butte has been known since the late 1800's. It was
of interest only to hobbyists until recently because people believed most of the opal was
unstable. Stability can be a problem with the opal, crazing can occur when stresses are created
from shrinkage due to water loss. West Coast has developed methods of drying the opal
that greatly reduce crazing. Even with the drying procedures, the stability
varies from 20% to 90% depending upon the variety. The opals are found in rhyolite geodes (thundereggs)
in a perlite that has altered to a pastel colored clay. The geodes that
contain gem-quality opal are only about 10% of the total geodes mined and only about 1% of the geodes contain
gem quality opal with play of color. The remaining geodes contain agate, quartz crystals,
or common opal. The geodes vary greatly in size, from a few centimeters in diameter to
over a meter. The deposit continues to produce a supply of very fine quality opal for
cutting and carving. Currently, a company has launched an American gemstone
jewelry line based on the Opal Butte's opal. Plans are to operate the
mine for at least the next 5 years