The opal is the national gemstone of Australia, which produces 97% of the world’s supply. The group of fine opals includes a large variation of gemstones, which all share one defining characteristic: they shine and sparkle in a continual change of color, which gemologists describe as “opalising”. Opals are classified according to the base or body color and the play of color that it displays. The five main types of opals commonly seen in gemstone trade circles are black opal, white opal, crystal opal, water opal and fire opal. While a lot of admirers consider the opal to be “out of this world”, there is some proof that this gemstone is just that. In 2008, NASA discovered opal deposits on Mars.
Hardness: Opals are not very hard, only achieving 5.5 to 6 on the Mohs’ scale of hardness.
Color: Opal’s internal structure allows it to diffract light and depending on how it formed, it has the ability to take on many colors. An opal color ranges from clear to white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Of these hues, white and green are the most common.
Birthstone: Opal is considered the birthstone for people born in October and under the sign of Scorpio and Libra.
Scarcity: Naturally occurring opals are rare but synthetics are much more common.
Value: The first step in evaluating an opal is determining the type of opal that it is, as each has a different price range. Red is considered the most valuable color. The next most important criteria for determining the value of an opal, is its quality “play of color”. The thickness of the opal layer is also used to determine the value as well as the beauty of the patterning, the cut, weight and finish.
Most Common Cuts: To bring out the best play of color in an opal, the stones are cut and polished into to round or oval cabochons. Only the best qualities of fire opals are suited for faceting.
Chemical Formula: The chemical formula for opal gemstone is a hydrous silicate dioxide (SiO2 + nH2O).
Synthetic Varieties: As well as occurring naturally, opals of all varieties have been synthesized. Pierre Gilson discovered the ordered sphere structure of precious opal in 1974, which led to its synthesis. The patches of color seen in a synthesized opal are arranged in a “lizard skin” or “chicken wire” pattern. Since this phenomenon can be observed only in a synthetic opal and not in a rough opal or a natural one, the property can be used to differentiate synthetic opals from natural ones. Furthermore, synthetic opals do not fluoresce under ultraviolet light.
History: Many ancient civilizations have held beliefs about the opal. The Romans valued the stone and used as a preventative medicine against “eye” disease, as well as a universal good luck charm. In the Middle Ages, a Holy Roman Emperor included opals in his crown and Shakespeare (1564-1616) mentioned the opal as “a miracle”. Queen Victoria (1837-1901) wore opals throughout her life and delighted in presenting them to her friends and to other royal family members.
The history of the opal spans back millions of years ago, when parts of Australia were covered by the ocean. Stone sediments were deposited along the shoreline and silica stone turned into opal. In 1849, the first opal blocks were found on an Australian cattle station. Soon after, the first opal mine opened there. Mining opals in the hot sun was not an easy task for opal prospectors.
Today, Australia is still home to 97% of the opal production in the world. Specifically, the town of Coober Pedy is a major source of opal. The remaining deposits of precious opal can be found in the Czech Republic, Slovakia, Hungary, Turkey, Indonesia, Brazil, Honduras, Guatemala, Nicaragua, the United States and Ethiopia.
Rumored Healing Properties: The opal has long been considered the luckiest and most magical of all gems because of its special display of colors. It is said to heal depression and to help find true love. Opals have long been linked to human emotions and are said to reflect the mood of the wearer. Opal is said to strengthen the will to live and treat infections and fevers. Purifying the blood and kidneys, opals are also said to regulate insulin.