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Australian Opals- A Primer

Australian Opals – A Primer


What has attracted people to opals over the centuries?  Colour, colour and more colour! 

Opals change colour when you look at them from different sides and angles.  Sometimes there is little colour at all and you move your head and suddenly a breathtaking burst of brilliant colour flashes from the stone.  There are very few natural gemstones which do that.


Unless you are lucky the more you pay the better the quality is.  But you can still get the high flashy colours for a lower price if you buy doublets or triplets. These are opal pieces reinforced with a solid backing of colorless opal.  A triplet has a clear dome of quartz or other material on top.


Opal starts off as a silica gel which seeps through sedimentary strata and gradually hardens over millions of years and the process of nature.  As an opal miner I have occasionally seen opal in this early stage where it is soft.  Opals contain a lot of water as much as between 3 and 10 percent.  On the Moh’s scale of hardness it co0mes in around 5.5 to 6.5 and that is relatively soft.


Australian opals are classified in several groups:

Black opals which come from the Lightning Ridge area in NSW.

White opals and light opals which come from the Coober Pedy region in South Australia.  These types also come from notable areas such as Mintabie and Andamooka.

Boulder opals comes from Queensland.


 Then there are some other minor areas which produce smaller amounts of high quality opal. 


Black opals have a dark base and white opals have a white base whereas Boulder has opal which is on top of or through an ironstone base.


Then you get various levels of blackness you might say.  So you might get an opal from either Lightning Ridge  or Coober Pedy which has a grey base.  That means that the stone has flashes of perhaps bright red and blue or other colours mixed inside of a grey base colour.  This grey base might be light grey or almost black.  When it reaches a very dark colour we normally call that a black opal.  It is like some childrens’ marbles that you see.


Then we have Crystal opal.  Crystal is transparent but the colours can leap out at you from this clear, see through base.  We also have varying degrees of crystal opal.  When we cannot see clearly through the crystal then we would classify it as semi crystal.


What does it cost?  It is very difficult to say what opal is worth.  We can weigh it and measure it but that doesn’t help until we can establish the quality. We look for the best pattern in the opal, the brightest colour and the most vibrant colour.  Red is generally the most expensive colour.  However, a small bight, vibrant green stone will command much more than a larger dark and dull red stone.  Since every opal is so different to the next it is very much a personal opinion.  Of course, people with experience will easily point out the major characteristics of a good or not so good opal.


Author: Gary Hocking

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