Australian Opal Types and Sources
Where does Australian opal come from?
The Australian Opal and Diamond Collection sources its precious gem stones from the world renowned Opal fields in Australia.Australian Opal gemstones are typically found at the following mine locations:
Coober Pedy | Andamooka | Mintabie | Lambina | Lightning Ridge | Opalton
Opal is a form of silica, chemically similar to quartz, but containing water within the actual structure. Precious Opal usually contains 6-10% water and consists of small deposits of silica spheres arranged in a regular pattern.
All Opal types have several shared scales that are used to describe gemstone features common to most if not all kinds of opals.
Perhaps the most prevalent of these are the scales describing an opal's body tone and transparency.
The body tone scale is used to differentiate a 'light' or 'milky' opal variant from the significantly rarer 'black opal'. any type of solid opal can be considered to be a black opal should its body tone fall within the body tone scale ranges of N1 to N4 inclusive, a Dark opal if the tone is in the N5 to N6 range inclusive, and light opal if within the N7 to N9 range.
Similarly, the opal's opacity is used to determine if an opal is considered to be a crystal opal or a milky opal, if light passes through the gemstone largely unimpeded
or in such a way as to dilute the opal's play of colour then it could be considered a crystal opal. If significant amounts of light is blocked from passing through (but often not all) then it would be considered a milky opal. typically the difference is caused by inclusions within the gemstone that block the passage of light through the silica, usually sands, while other inclusions such as plant or animal remains can also often form a part of the opal's structure, these will typically only influence the colour patterns.
A third scale is used to describe an opal's colour brightness, with brighter colour patterns being more highly sought after than dull colourations. the opal brightness is typically ranked into five categories labelled B5 to B1 - with B5 being the most vibrant and B1 being the least.
There are six significantly different types of opal to consider:
Black | Boulder | Crystal | Milky | Doublet | Triplet
We'll Start with the Layered Opal Types:
|
Triplet Opal
As their name would suggest, Triplet Opal gemstones are comprised of three distinct layered components
that together form a coherent gemstone. Triplet opals tend to exhibit broader and sharper colours for a much lower price point due to the comparatively smaller quantity of precious opal present in the final stone.
The first layer is a base of common opal, often reffered to as potch - this layer serves as the gemstone's foundation and allows the precious gemstone element to be set within a piece of jewellery. Secondly - a comparatively thin layer of precious opal gemstone, this is placed upon the foundation of potch to protect the precious stone layer from damage. Finally, the opal layer is covered by a protective and transparent capping layer - typically quartz, this layer forms the surface of the final gemstone and serves to further protect the precious stone beneath from damage. |
 |
|
Doublet Opal
As with The Triplet Opal, a Doublet Opal is comprised of just two layers combined with a process similar to that of a venire.
Firstly, a common opal backing stone (such as brown ironstone) is selected to serve as the base layer of the final gemstone, then a top layer of precious opal gemstone - usually a Crystal or Milky Opal gemstone wafer, is adhered to the surface of the base layer to form the final gemstone. |
 |
Solid Forms of Opal
|
Milky (Light) Opal
Commonly found in the mines of Coober Pedy in South Australia, Milky Opal is formed on a base of sandstone and potch.
the impurities this tends to introduce within the gemstone lead to a whitened, cloudy appearance - for which the opal is named. |
 |
|
Boulder Opal
Native to the state of Queensland and commonly mined from Quilpie, Boulder Opal tends to form in and around iron stone.
when opal forms with iron stone, the surface of the gemstone tends to become undulated, and can lead to long bands of flowing colour upon the host rock. matrix opal is also commonly associated with boulder opal types as the ironstone tends to dictate the formation of the precious gemstone, creating the matrix patterns within the host rock.
|
 |
|
Crystal Opal
Commonly Sourced from Andamooka and Mintabie within South Australia,
Crystal Opal is an entirely silicon based type of opal gemstone. this means that the crystal opals are often close to if not entirely transparent, allowing thier colour to filter through the entirety of the host structure. |
 |
|
Black Opal
Finally, from the region known as Lightning Ridge in New South Wales comes Black Opal.
These Opal gemstones form with varying degrees of Manganese Oxide within/as thier base stone. this tends to darken the appearance of the stone, often increasing the gemstone's colour contrast. A scale was developed to convey the degree to which this occurs for each individual gemstone - beginning with a rating of N4 which describes the lightest degree, through to N1 describing the darkest. though often darker stones are more valued due to thier colour contrast potential and comparative rarity the scale is more accurately used not as a direct measure for value but to help describe the features of the stone. |
 |