Types of Opal
When choosing an Opal, especially for the first time, its very important to understand that not all Opals on offer are the same. Some have taken millions of years to form and can last many generations. While other types of Opals are manmade and can lose their be colours within a very short time.Below is a brief guide on some of the more common types of Opals
Natural Solid Opal
Opals that has not been changed from its natural state -- except to be cut and polished into a gem stone. The best know types are Queensland Boulder Opal, Black Opal, Crystal Opal, White Opal. Opal can also be found in Mexico and Ethiopia. Natural Solid Opals are the most sort after types of Opals.
Australian Boulder Opal
Boulder Opal is uniquely found in small pockets of ground in western Queensland, Australia. Boulder Opal is a combination of an Ironstone or sandstone Boulder and a seam of Opal which was formed in the crevices inside the Boulder, often giving the Opal an uneven surface that further enhances the array of colours and patterns.
The material is cut and polished with the opal material still attached to the parent material (e.g. ironstone) on which the opal formed.
Side view of a Boulder Opal polished stones - notice the uneven way the opal and Iron stone has formed.
Boulder Opal Matrix – Are boulders or rocks where the brown Iron or sand stone has mixed with the Opal speckles, and where no opal seam has formed.
Example of Boulder Opal Matrix from western Queensland
Australian Black Opal
Australian Black Opal is one of the most well-known types of any Gem Stone.
A Black Opal has a black or very dark grey body tone or background to its appearance.
The darker the body tone of the Black Opal will mean the Opal colours speckles will stand out more enriching the beauty of the stone.
The most famous Black Opal mining area in the World is Lightning Ridge NSW, Australia.
Australian White, Light, and Crystal Opal
White opals have a white base, and the colour play and patterns present themselves in this white opal base. Opals in this category can host a wide variety of colours and light play patterns. White opals are the most common type of opal and can be found in all the Australian Opal fields. The Australian Opal Shop always has a good selection of white Opals and customers are amazed by the many colours.
Crystal Opal, the colour play presents itself against a transparent or translucent opal base. A rough rule is a printed page will be visible through the stone. Light can pass through a crystal opal and light opal. Crystal Opal can have the appearance of opal colours floating in the stone.
Koroit Opal Matrix
Koroit Opals are found exclusively in the opal fields of Koroit, Australia. Unique, artistic design and beautiful patterns of vibrant colour are characteristic of Koroit boulder opals. They make stunning pendants and rings, and they stand out in a any gem collection.
Koroit Opal Matrix set in Gold and Diamond Pendant
Australian Sandstone Opal Matrix
In some Opal mining areas of Australia, Opal can form in the Sandstone layers. This is called Sandstone Opal Matrix. This type of Opal Matrix, is found in western Queensland (another type is also found in Andamooka South Australia), can be cooked in cooking oil resulting in the sandstone becoming darker or black colour Cooking the sandstone matrix in this way will make the Opal colours look more vibrant and make any patterns formed by the Opal speckles more visible.
Natural Sandstone Opal Matrix Beads
Hydrophane Opal (sometimes called Water Opal)
Are Opals that have a large amount of water in their crystal structure normally around 17%. One of the characteristics of this type of Opal is when absorbed in liquids, its appearance can change.
If Hydrophane Opal is soaked in water, the water is absorbed into the Opal. As a result, any play of colour(fire) will seem to have disappeared. Colour will return once the Opals dries out. Direct contact to the skin should be avoid when wearing Hydrophane Opal, as the body’s natural moisture will be absorbed into the Opal, and colour lost.
Notice the Hydrophane Opal has become transparent after contact with water, and the Opal colours appears less.
Treated Black Hydrophane Opal
Although natural Ethiopian Black Opal has been found, when purchasing Black Ethiopian Opal today you must purchase on the belief that nearly all Black Ethiopian Opal have been treated. The appearance can look similar too natural Australian Black Opal but treated Ethiopian Black Hydrophane Opal will only be a fraction of the price.
Treated Ethiopian Hydrophane Opal polished beads
The Australian Opal Shop does not sell Hydrophane Opal
A doublet opal is comprised of two layers, a top layer of real, natural opal glued to a bottom layer of darker stone. Ironstone or black onyx is often used for this second layer.
A rough rule when purchasing Opal Doublet jewellery is that the value should be around 10% value of a Solid Natural Opal of similar quality and size.
The Australian Opal Shop does not sell Opal Doublets
Opal Doublet that has been chipped
Opal Doublet side view, notice that the join between the Opal slice and the brown sandstone rock is very flat and smooth, this is to make it easier to glue. Where as a solid natural Boulder Opal the join between Opal and host rock will be uneven.
A slice of Opal ready to be glued and made into an Opal Doublet
A paper-thin slice of Opal, glued on a stone backing, and a clear crystal dome top. After making, Triplet Opals will display bright colours, but can be ruined easily by getting wet regularly, eventually the glue that holds the Triplet Opal together will become cloudy and any Opal colours will disappear.
The Australian Opal Shop does not sell Opal Triplets.
A rough rule when purchasing Opal Triplet jewellery is that the value should be around 5% value of a Solid Natural Opal of similar appearance and size.
Opal triplet side view - 3 layers - can you see them.
(1.Top - glass dome, 2.middle - opal slice,3. bottom-- thin black backing)
A Opal triplet that has become cloudy and lost its colour
Synthetic and laboratory Opal (Fake Opal)
Man made resin, made to look like natural Opal.