8 Curious Facts About Opal Gemstone

The opal is an unusual gemstone that has a look to it that is unique in the gem world.  It is best known for its opaque white version. It also comes in a host of colours including colourless, yellow, red, orange, blue, green, brown and black. Let’s get to know a bit more about the opal gemstone.

Why do opals look like they do?

Opals look very different to most gemstone due to their internal structure; it diffracts light depending on the conditions it is formed under and this gives it the different colours.   The rarest colours are red against black while whites and greens are the most commonly found.  The density of the stone can vary from opaque to semi-transparent.

To use as a gemstone, opal is most commonly cut and polished into a cabochon.  Solid opal refers to where polished stones consisting wholly of precious opal whereas opals that are too thin to make a solid stone are combined with other materials to create gemstones.  

An opal doublet, for example, consists of a thin layer of precious opal backed by a layer of dark material, most commonly ironstone, dark coloured common opal, onyx or obsidian.  This dark backing gives emphasis to the play of colour and gives a better look.

An opal triplet is similar but has a third layer, a domed caped of clear quartz or plastic that is placed on top of the opal.  This heightens the polish and also protects the opal.  It can also magnify the colours of the opal but can be seen as having a more artificial appearance so usually aren’t classified as precious opal.

Opals are categorised as precious or common

Sounds a bit harsh but there are two categories of opal. Precious opals have a vibrant colour such as fire opals or have what’s known as a ‘play of colour’ where you can see different colours in the stone. If they don’t have this then they are described as common.

Opal has a hardness of 5.5-6.5 on th Mohs scale

The Mohs scale is used to show the hardness of stones compared to one another, with diamond being up the top followed by sapphire and ruby. Out of 10, opals are between 5.5 and 6.5 so more fragile than most of the birthstones. But if you take care with them, they can still make gorgeous jewellery.

There are different types depending on colour

Fire opal is a translucent opal that has warm colours, usually yellow, orange or red.  It doesn’t show play of colour apart from occasionally a green flash and is most commonly found in Queretaro in Mexico.  This gives them the name Mexican fire opals and they can sometimes be cut and polished because they tend to be harder than normal opals.  Mexica water opals are a colourless type of opal from Mexico that has a bluish or gold sheen.

Girasol opal has a bluish glow that follows the light source around due to tiny inclusions in the stone.  The main places the stone is found is in Mexico and also in Oregon.

Peruvian opal is also called blue opal, is semi-opaque, blue-green in colour, and found in Peru, as well as in Oregon and Nevada.

Black opals are one of the rarest but they aren’t always black and can be a number of dark colours.

It has a strong connection with Australia

It is the national gemstone of Australia with South Australia supplying around 95% of the world’s precious version of the stone. But opals are found around the world including in Brazil, Honduras, Ethiopia and Mexico.

Opals have been popular since Roman times

While the opals that the Romans used might have looked a bit different to the ones we find today, the basic stone is the same. The word opal comes from ‘opalus’ which literally translates to ‘precious stone’ so they clearly valued it.

The Middle Ages were a bit unsure about opals

In the Middle Ages, opal was considered to bring great luck because it combined the colours of all the other stones together.  It was also believed that if it was wrapped in a bay leaf and held in the hand, it could make someone invisible.

However, Sir Walter Scott’s novel Anne of Geierstein in 1829 showed opals in a less favourable light.  In the novel, the Baroness of Arnhem wears a talisman with supernatural powers that contained an opal but when a drop of holy water falls on it, it becomes a colourless stone and the Baroness dies.  This led to the stone being connected with bad luck and death.

More recently it was bad luck

By the 20th century, the opal was believed to be bad luck. Wearing it when it wasn’t your birthstone or buying it for yourself were two reasons it could bring misfortune. Opals got the blame for a lot of things going wrong although some of this could be down to the fact that it is a softer gemstone and more prone to damage.

October birthstone

Opal became the official birthstone for the month of October in 1912. The National Association of Jewelers in the US came together to confirm what people had already said since the 15th century – that it was the birthstone of October. It is also a gift alternative for the 14th wedding anniversary.

6 famous opals

Olympic Australia

The Olympic Australia is the largest and most valuable opal found so far, currently valued at A$2,500,000.  It was discovered in the Eight Mile opal field near the town of Coober Pedy, South Australian in 1956 just under 30foot under the ground.  It was named in honour of the Melbourne Olympic Games that were being held at the time.  It is 99% opal and has been left uncut and unpolished measuring 11 inches long, 4.75 inches thick and 4.5 inches wide.  It weighs 17,000 carats and is kept in the Sydney offices of Altmann & Cherny Ltd.

Andamooka Opa

The Andamooka Opal is a famous opal that was presented to Queen Elizabeth II in 1954 when she made her first visit to South Australia.  It has been found in Andamooka, South Australia, which has historically been an opal mining town.  It was cut and polished by John Altmann to a weight of 203 carats and has been set with diamonds in an 18 carat palladium necklace.

Flame Queen Opal

The Flame Queen Opal is the best-known example of an eye-of-opal, a style of opal when the stone in-fills a cavity.  It has a central raised dome that is either red or gold depending on the angle and is surrounded by a deep blue-green band. 

It weighs 263 carats and measures 2.7 x 2.50 x .50 inches.  It was found in 1914 at the Bald Hill Workings, lightning Ridge, New South Wales by three partners Jack Philips, Walter Bradley and Joe Hegarty.  It was exhibited in the Geological Museum of London in 1937 on the coronation of George IV and against in 1980-81.  It was part of the Kelsey I Newman Collection and is now part of the Jack Plane Collection.

Halley’s Comet Opal

The Halley’s Comet Opal is the largest uncut black opal ever found and is the third largest gem grade black opal recorded.  It was discovered in 1986 in lightning Ridge, New South Wales by the Lunatic Hill Mining Syndicate and was named for Halley’s Comet that was over the Earth at the time.  It weighs 1,982 carats and is around the size of a man’s fist.  It sold in 2006 for $1.2 million.

Other famous opals

The Galaxy Opal is the largest polished opal in the world bound in Boi Morto Mine in north-east Brazil in 1976.  It is 3,749 carats and measures 14 x 10 x 4 inches.  It is currently in a private collection.

The first named opal was called the Burning of Troy and was given to Josephine de Beauharnais by Napoleon I of France but is now lost.