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WK 4 Central Oz Trip Mintabie Opals

Sunday, July 07, 2013

We are in Mintabie Southern Australia this week looking for Opal. Mintabie is an opal mining community in the Anangu Pitjantjatjara Yankunytjatjara or "APY" Lands in South Australia. It is unique in comparison to other communities situated in the APY Lands, in that its residents are largely not of Indigenous Australian origin, and significant mining activity (of opal gemstones) is occurring.

Mintabie is situated 980 kilometres (609miles) northwest of the capital of South Australia, Adelaide. Mintabie is approximately 200 kilometres (124miles) south of the Northern Territory border. It has a permanent population of about 250, and was established in 1978. The average annual maximum temperature is 37.1C (99F) and the average annual minimum temperature is 5C (41F) Average annual rainfall - 222.6mm (8.8”). Mintabie is in South Australia and is close to the border with Northern Territory, in the very center of Australia, in very in-hospitable country. Living conditions are harsh and the environment does not lend itself to easy living. Water and provisions have to be carted great distances and under very trying circumstances Even with the introduction of very large underground water tanks things improved only marginally, and water is a very scarce commodity to be looked after carefully.

As with a lot of mining communities the populations grow and decline according to
whether large opals, or a good producing new seam are found in the area at that time!! Opal mining attracts a diversity of human characters often as colorful as the stone itself and they have one thing in common, ‘passion’. The thrill of finding precious opal is the driving force for these opal hunters.

In Mintabie the mines are open cut mines and worked with huge excavators. Because
the mines are worked with huge pieces of equipment “Noodling” is a very popular
past time of visitors and locals alike. This simply means going through the waste
heaps and finding pieces of opal that have been missed or crushed by the larger
equipment. Noodling is the practice of sifting through rejected mullock heaps for small pieces of precious opal inadvertently discarded by the miners. A number of people on the opal fields rely entirely on noodling for a living. They either sift through the waste material by hand ... or use a noodling machine. These people are 'professional' noodlers. Tourists and others casually searching the dumps of soil from the mines for pieces of opal are also "noodling". If you're going to noodle, you will first need a current Fossickers' Licence. As you might expect, a Fossicking Licence includes some restrictions. First of all, you may use hand tools only - no machinery is permitted. Hand tools are defined as picks, shovels, hammers, sieves, shakers, electronic detectors and other similar tools.

My van partner and I borrowed two sets of sieves shakers and a hand pick and short
spade from Ann's friend whom we called Opal. She owns a mine at Mintabie. The mines are famous world wide for their production of Opals, mainly white opal
but Mintabie also produces black and semi-black opal too. Along with Lightning Ridge in New South Wales, Mintabie produces most of the black opals in the world.

Opals are formed, rarely, when conditions are ideal, and spheres of silica, contained in silica-rich solutions in the earth form and settle under gravity in a void to form layers of silica spheres. The solution is believed to have a rate of deposition (the process of molecules settling out of a solution) of approximately one centimeter thickness in five million years at a depth of forty meters. If the process allows spheres to reach uniform size, then precious opal commences to form. For precious opal the sphere size ranges from approximately 150 to 400 nanometers producing a play of color by diffraction in the visible light range of 400 to 700 nanometers. A nanometer is one-billionth of a meter. To give you some perspective, a human hair tends to be between 80,000 to 100,000 nanometers in diameter.

Each local opal field or occurrence must have contained voids or porosity of some sort to provide a site for opal deposition. In volcanic rocks and adjacent environments the opal appears to fill only voids and cracks whereas in sedimentary rocks there are a variety of voids created by the weathering process. Leaching of carbonate from boulders, nodules, many different fossils, along with the existing cracks, open centers of ironstone nodules and horizontal seams provide a myriad of molds ready for the deposition of secondary minerals such as opal.

Black opals are the rarest and most sought after of the opals, because of their beauty. Black Opal is solid opal distinguished by the black or very dark body colour of the stone. There is a type of Semi black opal which has a body color of medium grey to a nearly black, but the darker the background the more the colors stand out and the more you can see the wonderful play of the color patterns as the shift and move across the stone. The brighter and sharper the colors in the background the more valuable the black opal is.

There are different classifications of black opal too. Here are what the rare ones look like:

Black Opals are my favorite type of Opal, and I like the Harlequin patterns the best of all. I am noodling this week hoping to find a few small fragments to have as a souvenir of my stay here. I have been waiting since the Bibbulmun Trek started to get to Mintabie and see the black opals they sell. I am not a big jewellery fan but I would like to one of a fragment big enough to be set in a small ring, or perhaps a pair of earrings.

A true Harlequin pattern is a repeating pattern of contrasting diamonds or elongated squares displaying color. Some one could mine for opal for a life time and only be lucky enough to find one or two Harlequin black opals as they are such a very rare and valuable pattern. Barry O'Leary, who is an author about opals defines the Harlequin as "Precious opal showing a regular mosaic-like chromatic pattern in rounded, angular, or roughly square patches of about equal size, presenting a spangled appearance."

They are all unique and are divided in to several different pattern types. Below are
two photos explaining the different patterns and showing some very rare and beautiful ones on sale through Opal Auctions online:

There are about 9 main types of opal found and sold today.

Top From left to right—black opal, white opal, crystal opal, fire opal,
Bottom from left to right—Yowah nut, matrix opal, boulder opal, doublet, and triplet.

Opals are a living stone, meaning that it needs protection from heat and detergents that can dry out the gem. This means that the opal will have or had a problem with humidity. Opal is a gem that contains water and needs to be stored in an atmosphere which is humid enough for the opal not to loose its water. If the opal loses its water a network of tiny cracks can appear called "crazing". Of course as a result it will lower the stone's value. They develop crazing if they are allowed to dry out. Opal crazing is a very serious matter. Sometimes opals may have been stored in a humidity-controlled safe deposit box at some point and get deprived of the atmospheric moisture needed to replenish slight normal dehydration. NEVER store opals in bank vaults!

It took the development of the electron microscope to work out how Opal color is produced. Precious opal is made up of tiny uniform spheres of transparent hard silica, which fit together in an orderly three-dimensional frame, sitting in a "bath" of silica solution. It is the orderliness of the spheres that separates precious opal from common opal. Light passes through the transparent spheres in a direct line, but when it hits the 'bath' of silica, it is bent and deflected at different angles, thus producing a rainbow effect. Deflection and diffraction happens depending on the size of the spheres, in which varying colors of the spectrum are diffracted. So it is a combination of deflection (bending) and diffraction (breaking up) of light rays that creates the color in opal. If you move the stone, light hits the spheres from different angles and brings about a change
in colors. The name opal actually means "to see a change in color." The way in
which colors change within a particular stone as it is rotated and tilted is called the stone's play of color. The size of the spheres has a bearing on the color produced. Smaller spheres bring out the blues, from one end of the spectrum. Larger spheres produce the reds from the other end. The more uniform the spheres are placed, the more intense, brilliant and defined the color will be. Here are two beautiful pendants with a flash opal and a black opal that show the spectrums:

During the week we all noodled in the open dumps of soil from the mining which has
fragments in it from the seams of opal mined. This is what people are looking for,
some hoping to make a living from what they find, and some hoping to find a lost very rare and valuable opal, such as the Harlequin patterned black opal. The chance of that happening are equally as rare as the black opal is. Some one can mine for a lifetime and be lucky to find one or two really top quality Harlequin opal.

On the third day of this week Opal and Ann planned a surprise for us. Opal took us down in her mine - to see a seam they have found. Because its a busy and dangerous place - and can be a tight fit in places - we needed to go in groups of 2 or 3 only. She also said that right under the seam there was loose soil and there would be chips there. We needed to work quickly in there as there were other groups waiting to come down and the machines couldn't work while we were there. Since some of us didn't have too long down there and so didn't find anything Ann told us "Don't worry if you didn't get anything or didn't get time - Opal will bring the lose soil out later tonight and you can noodle in it tomorrow!!

I got to see how the opal develops in seams and they have to cut along the seams - and how fragile the stones are. Because I was so very interested in black opals she showed me a picture of what a thick seam of black opal looks like in the mine:

It made me noodle all the harder while I was there. And I did find some little fragments while I was there. Only two of them were very tiny black opal pieces, I will cherish them but they are of no value to anyone but me.

There are a lot of shapes and conditions to buy stone in, rough or cut and polished, the ones in Mintabie and elsewhere in Australia are usually domed. The opals can be cut into a wide range of popular shapes. Oval is by far the popular shape, followed by the circular or round shape. Teardrop, square, rectangle, and triangle are other common shapes.

Most people think of opals as gems set in jewellery pieces. Here are some of the types of pieces that are used for opal jewellery:

It was a wonderful week, an experience I will never equal and the noodling was fun! Some of us bought opals from Opal, and had them set in various pieces to wear. We all found some little pieces and Opal was kind enough to set them into resins or key chains for us. I love the small opal chips I found. Opal is polishing them and setting them into a silver bird cage like pendant and silver chain so I can show them off. I found two beautiful pieces of boulder opal, again two small to be valuable, but a little larger than the fragments, and a beautiful tiny piece of an opalized fossil of a shell, which she is setting in a small domed resin paperweight. This is a blow up of two different opalized fossil shells much like the fragment I found only they are way larger than the fragment.

She had a wonderful small fiery harlequin black opal for sale and a really fine crystal opal that would have been perfect for rings or as pieces in a bracelet I admired them greatly but they were of the kind that are really expensive, anywhere from 800 up to 12,000. But if any of you are interested in really beautiful Opals Mintabie sells opal on line, even on Ebay and the auctioning is exciting to bid on. Here is a link to some displays of opals at Opal Auctions: www.opalauctions.com/mu

And here is a link to the opals Mintabie currently has up for auction at Opal auctions:
Some of the opals are as low as 25 US dollars and some range up to 12,000 USD.

We ended the week there by having a BBQ for the town - to thank them for all the hospitality we were shown. We were allowed to use the BBQ facilities behind the pub, and Ann got a lot of necessary things in Marla the day before. As well as ordering meat and salad vegetables from Alice so we had food for the BBQ. The rest of us gave her help doing salads and things like splitting and buttering rolls and fruit salad, as well as vegetable salad to be made too to make! Also we needed to organize shifts for cooking on the BBQ - as people will wander in and out - and those miners really have appetites! I'm good at serving up food to people so I floated between serving up food on the plates and carrying plates out to the people and replacing napkins and forks and the like.

Mintabie is a world all of its own. Easy indeed to see how people can get into this opal finding obsession and spend their whole life looking for the shiny pieces that will make them rich. I can't afford them, not the beautiful black harlequins that are so very rare and beautiful and extremely expensive. But now that I know they are there I can dream..... maybe some day!

Here are some other beauties of the opal world to leave you with: These are some very rare Tomato Opals found at Mintabie by a miner there. They are amazingly hard to come by! Here is a beautiful Black Harlequin: And a Vintage Gold Fiery Harlequin:

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Member Comments About This Blog Post
    Wow, who knew. I am so impressed with this blog. I could never get that much information out- and with pictures no less! Super impressed. I don't work well with small phones, and am trying to limit sitting at a computer so much ( not succeeding, been here catching up on blogs for long, long, time). Thanks for sharing. I have a daughter with opal as a birthstone, plus I just tried mining gold-not as easy as I thought. Very interesting blog.
    1783 days ago
    I never knew how opals were mined! emoticon chris
    1784 days ago
    What an instructive and enjoyable blog - thank you for the work you've put into this post. I learned so much! I have a little set of white opal earrings that I love but I had no idea there were different colours/kinds of opals. Well done!
    1784 days ago
    emoticon It really was a Beautiful Experience!! the Opals were so pretty and such a Nice reward for all the Dirty, Dusty work to get them!!
    emoticon Kind of makes one think about the "Dirty, Dusty Work" of changing Our Eating & Activity Habits. It is NOT "Fun" but the Results are More Than Worth It!!
    1784 days ago
    Wow, Kacey, That was really a good Blog. Beautiful Opals!

    1784 days ago
    Good blog -= heaps of info!!
    This was the one I thought you might enjoy the most so I'm glad you eventually caught up with it
    1784 days ago
    How beautiful.
    1784 days ago
    Another Trek? You're certainly keeping busy these days! Interesting information and beautiful opal pictures. My first husband used to go opal mining in Nevada with a friend when we lived in Oregon. They didn't find any but the terrain sure looked similar. Hope you're enjoying your virtual visit.
    1785 days ago
    emoticon emoticon emoticon
    1785 days ago
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