How is opal formed;
Over 100 million years ago inland ocean ran through central Australia, when the oceans water descended/evaporated the remaining pockets of water soaked in through the earths ground.
The water picked up silica from sandstone & this silica-rich solution filled in through cracks and voids caused by natural faults or decomposing fossils. As this water evaporates, it leaves behind a silica deposit & over millions this turned into opal
Australian Opal are found in & around the edges of the Great Artisan Basin in central & remote areas of Australia
What gives Opal its colour/s and patterns?
When the chemical properties of opal are forming, they form in balls/spheres.
Spheres of a small to large size, that are consistent & fairly even in shape, size & placement produce better quality opal
Spheres that are too small, inconsistent in size, shape & placement will produce commercial, lower grade – potch quality opal
It is then the diffraction of light bouncing off & through the spheres & gaps between that determine the overall quality; colour/s, patterns, depth, intensity.
What is potch?
Potch is colourless opal, it has the same chemical make up as opal & while it does have colour (it can be grey, white, black, orange, blue, caramel, tan/neutral tone) it has no colour play or lively colour. It is a solid, base tone. Potch on its own does not hold any value.
There are many opals that will have formed with both precious opal and potch, in this instance when formed in particular aesthetically pleasing ways there can be value in keeping the potch apart of the whole opal as it has created a unique design.
With other types of opal, Lightning Ridge Opal & White Opal they are often formed encased in potch and the potch is the back of the opal, in the same way that Boulder Opal has the host rock.
Australian Opals hardiness;
Australian opal hardness on the Moh’s scale;
Australian Opals range from a 5.5-6.5 out of 10
This is harder than pearls but softer than diamonds, emeralds, sapphires or rubies
Boulder Opal with host rock tends to fall into the hardier side of the scale as the host rock provides further durability, with ironstone host rock being the overall sturdiest host rock
Australian Opals are non-porous;
Australian opals are formed with around 5-6% water content, this is immersed into the silica structure during formation & do not absorb any further liquids.
Australian Opals are non-hydrophone/non porous & will not be impacted by water
Doublets, Triplets, Treated & Synthetics; We do not sell any of these.
Though it is important to be aware of these when shopping for opal
What are Doublets;
Doublets consist of two layers adhered together with glue:
A paper-thin slice of opal cut from a solid opal & a backing which can be a variety of different material including; black industrial glass, black or grey potch (colourless opal), hard plastic, brown ironstone or sometimes vitrolite.
Triplets;
A triplet is the same two layers as a doublet but also has a domed top glued onto the opal. A clear glass, quartz, or plastic capping in the shape of a dome.
- They are a man-made product using a small percentage of natural opal
- Doublets & Triplets cannot be wet or in areas of high moisture as over time the glue can start to separate from the layers causing the opal to appear foggy.
Treated Opals; These are natural opals that have been ‘treated’ to enhance the opals colour and/or fill (hide) cracks in opals
There are a variety of different ways to treat opal, the outcome being for the same purpose, to make the colours appear brighter/more valuable than they are or to hide a fault.
There is nothing wrong with liking or wanting to purchase treated opals (if that’s your interest), as long the business selling them has correctly & transparently declared the opal as treated & the price should be reflective of that
Synthetic opal; Synthetic Opal is a man-made/lab created product
