Opal: The Queen of Gems
Opal, the birthstone for October, is one of nature's
most prized gems. The stone - which also happens to
be the recommended jewelry gift for couples celebrating
their 14th wedding anniversary - was mined by eastern
Europeans, the Aztecs and the ancient tribes of Central
Africa. Opals have been featured in the crown of the
Holy Roman Emperor and the crown jewels of France. They
were mentioned in the plays of Shakespeare and the novels
of Sir Walter Scott. Napoleon gave an opal to Josephine.
Queen Victoria gave them out as wedding gifts.
One of the reasons this gem has been so revered is
because of its supposed mystical powers. Scandinavian
women wore opals in their hair to prevent it from going
gray. The Arabs thought opal would ward off lightning
and grant invisibility to its wearer. Other powers ascribed
to the gem include the ability to grant vigor, aid the
heart and kidneys and protect against fainting and infection.
Worshipped by the Romans as a symbol of hope, fidelity,
purity and good luck, opal is sometimes called the "queen
of gems" because the stone can flash patterns of
color representing every hue of the rainbow.
This "play of color" is one of opal's signature
characteristics. The gem is found in a range of hues,
including white opal (the most common); black opal;
"boulder" opal (black opal with iron oxide);
crystal or water opal, which is transparent; and fire
opal, which has a yellow to orange to red body color.
The vast majority of the world's opal supply comes
from Australia. Black opal is the rarest variety and
therefore the most valuable. White opal is also mined
in Brazil. Fire and crystal opal can be found in the
United States (Nevada) and Mexico.
Brilliance of color and color pattern are critical
in determining the value of opal. Opals with strong
flashes of red fire are generally the most prized. Stones
with blue or green flashes are more common and subsequently
less valuable. Stone size also helps determine price,
since the gem is very rare in larger sizes. Prices can
vary from a few dollars per carat for common white opal
to more than $1,000 per carat for fine black opal. Most
stones are not faceted and usually cut into rounded
cabochons to enhance color play.
Perfect natural opals are extremely rare and expensive.
Many are treated to enhance their appearance. One common
technique is to place the opal in a sugar solution and
then in sulfuric acid, which blackens body color and
makes the play of color more pronounced. Other treatments
include applications of colorless oil, wax and resin;
plastic, or synthetic resins and hardeners to fill cracks
and improve durability.
With a hardness of approximately 5.5 on the Mohs scale,
opal is relatively fragile, and care should be taken
not to scratch, chip or crack it. To clean opal, use
a soft cloth moistened with olive oil. Do not use chemical
or mechanical cleaners. Also, avoid heat and dry conditions
that could dehydrate and crack the stone. Avoid impacts.