The opal fields of Australia were formed at the bottom of a large inland sea. In this sea there were all sorts of marine creatures including turtles, crocodiles, dinosaurs, all sorts of fish and of course shellfish. As these creatures died their bodies sank to the bottom of the sea and were covered with sand and silt. Over millions of years the sea dried up and various clays and sand were deposited over the sea bed. The bodies of the sea creatures obviously rotted away and the bones and shells, being made of calcium carbonate, were dissolved by acids in the soils. This would have left cavities in the shape of the dissolved creatures. Silica then seeped through fissures and cracks and filled these cavities which acted as casts for the silica that filled them. In some cases the silica turned into opal and the reult was opal in the exact shape of the shell or bone that had been deposited on the sea bed so long ago.
It was all very good finding opal in the early days but if no-one wanted to buy it, then there was little use risking your life trying to find it. Still this did not deter the brave souls who ventured into the harsh environment of central Australia to chase opal. In the 1880's opal had been found in Queensland and miners had established themselves in various areas where opal had been found. At that time they realised they had found a valuable and rare gem but there was no-one to buy it. Miners would hoard the best quality opal and throw away the more inferior material. There are records of miners with sugar bags full of top quality opal but it was of no use to them in outback Queensland.
Yowah is a small town in south west Queensland and is famous for the Yowah Nut which is only found here and nowhere else. The yowah nut is a relatively small, hollow ironstone concretion in the shape of a nut. They occur in closely packed horizontal layers with sandstone overlaying these beds of nuts. In some cases the centre can be filled with gem quality opal but in most cases they are filled with air, powder or some other non valuable material. Yowah also has some really beautiful matrix opal which is the same ironstone concretion often with small flecks of precious opal interspersed through the ironstone.See my post on Yowah Nuts post for more details.
White Cliffs is famous in Australia as an Opal Town but it is also unique for another reason. It was the site for world's first experimental solar station for supplying power to small outback towns.
In 1979 New South Wales was experiencing major political problems. Premier Wran believed that a major environmental project for the state would improve his party's popularity and he had in mind a likely project. The oil crisis in the 1970's had everyone talking about alternative fuel sources so the time was ripe for a solar energy trial.
Yowah is a small outback opal town in Queensland located about 1,000 km west of Brisbane and about 130 km west of Cunnamulla.There is a sealed road all the way so it is very easily accessible. The opal field surrounding Yowah is quite small, being about 4 square kilometres. It has all the amenities you need for a fossicking holiday. There is a store, cafe and two camping grounds. (one where you have to pay fees and a free campground with showers and toilets but you have to pay for the showers). The paying campground has a bathhouse attached where you can loll in your bathtub sipping a glass of champagne looking up at the sky. The only downside is that the tubs are filled with hot artesian water straight from the bore and it does have a maloderous smell. That is it stinks of sulphur. But apart from that it is a great experience and well worth it after a day of dusty fossicking.
It seems that the discovery of opal in Australia was often due to chance with many of the discoverers either looking for something else or drilling for water in the outback. When we understand how opal was formed it is not a surprise. Most opal is buried deep beneath the earth and it is only possible to find it on the surface if the earth has been weathered by wind and rain to a level below the opal layer. When this occurs pieces of opal can become exposed. These are called floaters as they also can be washed away by the elements and can end up a long way from where they were originally formed. Finding of these floaters often led to the discovery of a field. If erosion has not reached the opal level there is no way of knowing if opal exists unless a hole is bored. This is expensive and very much a hit and miss method as opal is often scattered in small pieces over extensive areas.
If you have any thin pieces of opal with nice colour but believe it is too thin to cut a cabechon then think about making a doublet.
A doublet is basically a fairly thin layer of usually opal glued to a thicker layer of opal potch or some other material to make a stronger stone. A cabechon is then cut from the prepared material. Don't be afraid to have a go at making doublets. It is not too hard and you don't need a lot of equipment. The equipment you will need, in addition to opal cutting equipment is as follows:
While my main interest is in opal and the opal towns, I still can't resist visiting some of the old gold mining towns as they share a similar kind of history. It never ceases to amaze me how seemingly intelligent men (and it was mainly men) would give up everything and undergo great tribulations to look for gold in some of the most desolate places on earth. Unfortunately, gold seems to have been formed in areas where weather conditions are extreme. The Yukon in Alaska and the deserts of Australia are striking examples and even areas in Victoria such as Ballarat and Bendigo are known for their extremes of weather.
Barbara and I love to travel in the outback. We don't go in for the arduous 4 wheel drive trips, crossing sand dunes and putting ourselves at risk, but we do love to head off and see where our travel takes us. In 2004 we set off up the Oodnadatta Track because it was somewhere we hadn't been before.We were driving a 1996 Toyota Hilux and towing an old off-road camper trailer. Having reached Coward Springs, an old railway station site on the original Ghan Rail line with a lovely hot artesian spring, we were told of a wonderful place to visit called the Painted Desert. So, after reaching Oodnadatta we set off for Painted Desert and were not disappointed as the colours of the hills were amazing with reds, whites and yellows abounding. As we were so close now, only about 200km, we, or maybe I should say, I, thought we should call in at Coober Pedy again as we hadn't been there for a while. This tends to happen a lot whenever we get close to an opal field. Barbara agreed and off we went.
If ever you travel through any of the opal towns it pays to stay awhile and talk to the locals. For some reason these places attract some of the real characters from all around the world. If you are looking to buy a small parcel of opal it gives you a reason to talk to the miners and they are often willing to tell you a little about themselves although not all of them will open up. We have been lucky to meet some of these characters on our numerous trips. One of the most interesting was Crocodile Harry.