BY DYLAN MORTON MINTABIE OPAL MINING

It is 268km from Coober Pedy. As in many other part of South Australia, Aborigines were reportedly the first people to find opals at Mintabie. They sold black opal at Coober Pedy during the first world war but it was many years before miners braved the harsh conditions to mine in the area. The first miners to work at Mintabie found the sand stone to hard to successfully mine. Later in 1976 when large machinery was introduced, the excellence of Mintabie was fully realised and the new township was established. INTRODUCTION

HOW DO THEY FORM? Opal is made from a material called silicon. It has water stuck to the silicon molecules and this makes it different to sand, because that is made from silicon as well. Precious opal forms when the silicon molecules arrange themselves in regular patterns. When the silicon molecules make random patterns the opal has no colour and is called potch which has little value. Opal’s were formed millions of years ago when some of the silicon seeped into cracks in clay. Which was at the bottom of a big inland sea, which covered a lot of Australia.

WHERE ARE THEY FOUND? The most famous places to find opal are Lightning Ridge, Coober Pedy, Mintabie, Andamooka, White Cliffs, Yowah and many more places.

WHAT EQUIPMENT IS USED TO MINE IT? At Mintabie, the early miners used pick and shovel. In later years the miners made all sorts of machines to do all the hard work for them. Rotating digger machines, which ground away at the tunnel face was a very helpful tool. When the miner heard a sound like breaking glass, he or she would stop and see if there was any opal. A truck would then take all the dirt and clay to a cement mixer where any opal would get separated from the dirt and clay. Then all that was left was bits of opal.

HOW DO YOU VALUE IT? Generally red colour is the most valuable then orange, blue, green and then violet. Black opal with red flashes can be valued at more than $5000 per carat. A carat is one fifth of a gram, which is really small. The real value of any opal is what the buyer is willing to pay for it.

INTERESTING FACT The "Olympic Australis" is said to be the largest and most valuable gem opal ever found. It was found in 1956 at the "Eight Mile" opal field in Coober Pedy. A miner found the opal at a depth 30 feet below the ground. It was named in honour of the Olympic Games. Which were being held in Melbourne at the time. This opal consists of 99% gem opal with an even colour in it, and is one of the largest and most valuable opals ever found. It weighs 17,000 carats (3450 grams) and is 28cm long, with a height of 12cm and a width of 11 and a half cm wide. It was valued at $2,500,000 in 2005.

BIBLIOGRAPHY John Dodson

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