Sunday, December 14, 2008
The Opal has always been somewhat mysterious to me...the way the stone changes color when you look at if from different angles, with flashes of blue, green and red! I found out these are called precious Opals and not all Opals have this wonderful appearance, but more of that later.
Above are two Opal rings of mine, as you can see, the ring on the right has a great deal of flash the one on the left not so much!
I've read two opinions as to the source of the name, one is the Opal takes it's name from a Sanskrit word for "stone", the other is the name is derived from a Latin word "opalus and a Sanskrit word upala which combined means "precious stone"...the opinion makes sense to me!
Up until the end of the 19th century Slovakia supplied Opals of the highest standards, now the primary location is Australia, found around New South Wales, South Australia and Queensland. Other deposits have been found in Brazil, Guatemala, Honduras, Indonesia, Japan, Mexico, Russian Nevada and Idaho.
In 2000, the Australian Gemstone Industry Council developed an system of names and classifications for opals which has been accepted worldwide.
The two basic categories are:
Precious Opal: this is any Opal showing a play-of-color. My two rings above are Precious Opals. With in this category are types of precious Opals,Type 1, Type 2, Type 3, Doublets and Triplets. The difference between Types 1, 2 and 3 is how the Opal has formed in the stone and how and in what stone it is found. The Doublet and Triplets are assembled stones, while they do contain a layer of natural Opal they are not considered natural Opals.
Somewhat confusing... I know!
Common Opal or Potch Opal: while these particular Opals share the same composition of Precious Opals they lack the play-of-color present in the Precious Opals...they are rarely transparent and often opaque.
Below are six large white common opal stones from my stock.
Here is an interesting quote from Galleries.com which explains much better than I could how the flashes are formed...
"Opal has been a popular gem for many centuries. It has the same chemical formula as quartz with the addition of 5 to 10% water. Structurally it consist of tiny spheres with water filling the gaps. These spheres in most Opals are irregular in size and inconsistent in concentration. Yet in Precious Opal, the variety used most often in jewelry, there are many organized pockets of the spheres. These pockets contain spheres of approximately equal sizes and have a regular concentration, or structure, of the spheres. This has the effect of diffracting light at various wavelengths, creating colors. Each pocket produces a different color, with the different intensity depending on the angle from which a viewer sees it. The multicolored flashes of light that the Opal emits give it a truly beautiful and valuable look."
95% of Opals minded from the Opal fields are classified as common opals, which means they have one color, such as white, grey and black. Of the 5% with color most of those are low grade so only 0.25% of Opals mined have any real value. Seems such a small amount for such hard work!
The yellow common Opals on the right are also from my stock.
Here is a simple explanation of how Opals are formed from Opals Down Under!"Opal is formed from a solution of silicon dioxide and water. As water runs down through the earth, it picks up silica from sandstone, and carries this silica-rich solution into cracks and voids , caused by natural faults or decomposing fossils. As the water evaporates, it leaves behind a silica deposit. This cycle repeats over very long periods of time, and eventually opal is formed."
For those of you who aren't familiar silicon dioxide is commonly known as quartz or sand...
Again...the common Pink Opals on the right are from my stock...
As always... I've enjoyed delving into the world of stones...finding fascinating information and passing it along to everyone...
Gemstones of the World, Walter Schumann, Third Edition, Sterling Publishing Co. Inc.,
The Jeweler's Directory of Gemstones, Judith Crowe, Firefly Books, 2006