Different types of Opal
The main varieties of Australian Opal available are listed below
Black Opal
Precious Opal that has a black appearance when viewed from the front. Only Opal that has a body tone of N1-N4 can be called Black Opal. Rarer than light or dark Opal.
Origin :Usually Lightning Ridge area in NSW or more rarely Mintabie in South Australia.
Dark Opal ( semi black opal )
Precious Opal with a grey or darkish appearance when viewed from the front. Dark Opal is relatively abundant.
Origin : Usually Lightning Ridge area in NSW or Mintabie in South Australia.
Boulder Opal
Usually a thin layer of precious Opal naturally adhering to brown ironstone host rock. Relatively abundant.
Origin : Queensland Opal fields
Crystal Opal
Translucent appearance – a printed page would be roughly visible through the stone. Relatively abundant.
Origin : Most Opal fields
Light Opal
White or light in appearance. Most abundant and affordable.
Origin : Usually South Australian Opal fields and also found in some from other areas.
Andamooka Matrix Opal
Black or darkish bodied Opal with bright specs of colour. This is chemically treated Limestone matrix with precious Opal in voids. Not common.
Origin : Andamooka Opal field in South Australia.
What is Black Opal?
A Black Opal is a natural solid stone with a black or nearly black body tone (i.e. background appearance).
Whether an Opal is a black or not can be determined by merely closing ones eyes and squinting at the face of the stone. All colours are ignored and the overall body tone (blackness level) can then be seen. When this is compared to the scale of blackness shown below it is possible to identify how black the stone is.
Only stones achieving values N1 to N4 on this scale are considered Black Opals – attracting the additional value associated of this class of Opal.
What Determines The Price Of An Opal ?
With each Opal it is important to consider the following –
- Colours present in the stone which is also called ‘play of colour’
- Brightness of the stone also referred to as the ‘fire’
- Whether the stone is black, dark, boulder or light body tone
- The care of Opals and Opal jewellery
- How saturated or intense the colours are
- Whether the stone appears dull from any angles
- Whether the stone is flat on top or has a rounded dome
- The size and weight of the stone
- The cut of the stone – even oval or irregular free-form
- The value of the setting the Opal is in, if set – the gold, accent diamonds and workmanship
Opals that have mixed spectral colours of red, blue, green are the most valuable, often fetching many thousands of dollars per carat, particularly if they are bright.
However, there are many stones in blue and green that can range down to as low as $20 per carat retail. Brightness and fire is major consideration, driving up the value if the stone is very bright.
Doublets are typically one tenth the value of the solid equivalent, with triplets being even cheaper.
If looking at stones and Opal jewellery pieces in various outlets it is important to compare “like with like” – to consider whether particular stones have the same brightness, same play or colour or quality of setting and whether other considerations such as the showroom lighting are the same, when checking prices.
In addition to solid Opal, a number of other varieties composite Opal are widely available. Composite stones are generally more affordable than solid stones as smaller amounts of precious Opal are used. In all cases, thin slices of Opal are glued to a backing of black backing material.
While most composite stones are made from natural Opal, occasionally synthetic Opal is used in doublets or triplets. Consumers should ask the supplier to confirm whether Opal used in composite stones is natural. Also note that whilst composite stones generally have the appearance of black Opal, none can be correctly described as Black Opal.
Opal Doublet
Thin slice of precious Crystal Opal glued to black backing material. When the backing is brown ironstone it is often called a Boulder Doublet.
Opal Triplet
Thin slice of precious Crystal Opal glued between a crystal cap on top and a black backing.
Mosaic Opal
Thin chips of precious crystal Opal glued onto a black backing. It can be used in Opal Doublets, Triplets or on watch faces.
Inlay Opal
Small thin pieces of precious crystal Opal glued directly into channels in jewellery.
Questions to ask when buying an Opal
It is important that you receive accurate and complete information from your vendor.
For example, you need to clarify whether a stone is a natural solid, composite(doublet or triplet) or synthetic and whether it is a light, crystal, dark, black or a boulder Opal.
The vendor should be able to supply a certificate confirming the authenticity of the stone in relation to these features, the weight, dimensions and the purchase price.
How to Care for your Opals and Opal Jewellery
Opal jewellery requires no greater care than other jewellery mounted with stones such as Diamond, Ruby, Emerald, Tanzanite or Turquoise.
You should never wear any jewellery in rough conditions such as to the beach or during activities where it may get knocked by metal or hard objects (e.g. washing up).
In these conditions, stones get dislodged from their settings, gold gets scratched and stones get chipped (even diamonds) and Opal should be treated the same as all other stones – with respect.
Opal requires no special treatment or care. As with other stones, grime from wear can be wiped off with a damp tissue or cloth.
( Source : Australian Opal Association Inc .)
