Lightning Ridge
Black Opal
Black opal is mined in and around Lightning Ridge in Northern NSW and usually has a black or
gray opal base on the back of the gem.
Lightning Ridge was discover by local
grazers and passing drovers in the 1880's and has been mined continuously since its discovery. Due to its long history and consistent production, the world market has come to admire this magnificent gem. Hence the Lightning Ridge Black Opal is said to be the most valuable with prices sometimes reaching over AUD$20,000 per caret. The best quality black opal (red on black base) is more expensive than diamonds. It is extremely rare and of supreme beauty.
White Opal
White Opal is minded in and around Cooper Pefy, South Australia, and as the name suggests has a
light-colored white or translucent base with a sparkling show of pastel
colors.
White opal was first discovered in the 1840's at White Cliffs, however it was not until 1889 that the first big rush began. Development at Coober Pedy commenced in 1915, followed by Andamooka in 1930 and Mintabie in 1931. Nowadays, these fields combined account for over 80% of all Australian opal production.
The Rare & Beautiful Opal
Australia is renowned for the world's finest opal, with 95% of the total worldwide production originating from the rich mineral deposits scattered around the eastern edges of the Great Artesian Basin. More than 80% of Australia's total production of gem quality opal is white opal with the very rare and beautiful varieties of boulder and black opal making up the remainder.
Opal is one of the rarest of precious gems, its annual production is far less than diamonds, sapphires and emeralds. Added to this, the Australian opal has a most unique appearance, characterized by a display of sparkling prismatic
colors as the stone is moved through different light.
Our Prehistoric Gem
Opal was originally formed during the
tertiary period of history, some 15-30 million years ago. Before it became the beautiful gemstone we know today, opal started as a liquid gel which seeped through the top sedimentary layers of the earth until it reached the impervious clay level some 30
meters down. Here over millions of years, this liquid gel hardened to form deposits of precious opal.
What Is Opal?
Scientifically, opal is composed of minute particles of silica, closely packed in transparent spherical arrangements. Light passing through these spheres is scattered, causing the diffraction of white light
into its various base colors of red, orange, yellow, green, blue, indigo and violet. This is similar to the effect of a rainbow or white light passing through a prism.
In chemical terms, opal is made up of hydrated silica with a varying water content between 6-10%. The chemical composition is Si O2 n H2O. Opal is the only gemstone with an amorphys noncrystalline structure, typified by a random irregular pattern. This is one reason why no two opals ever look the same.
Buying Opals with Confidence
There are many factors determining the value of an opal, some of the most important being brilliance of
color, color pattern and color play. Other factors to consider are the type of opal, its size, shape and the rarity of the stone. The first step in choosing your opal is to select a
color that appeals to your own personal taste. Whatever your preference, Australian opals provide a myriad of choices in all combinations of
colors, shapes and sizes. Each opal is unique, but you will know yours as soon as you see it.
What are Doublets and Triplets?
All opal formed naturally is known as "natural" or "solid" opal. This is still the case even when the stone is not opal all the way through, but has a natural backing of potch or ironstone. Most solid black opals and
boulder black opals are cut with some of their original potch or ironstone concretion left in place on the back to give the opal more strength for setting and provide a dark background for the
colors of the opal.
Since the 1960's some synthetic and manufactured forms known as Gilson, doublets and triplets have also been developed to have an "opal-like" appearance. Doublets and triplets are not solid opal all the way through and are manufactured by laminating a thin slice of light opal onto a black plastic or potch base and then adding a clear quartz dome on the top in the case of triplets. These man-made forms can be extremely sensitive to water, humidity and heat, which may cause the different layers to separate. However they can be very beautiful as costume jewelry and are often sought after as souvenirs.
