All You Need to Know About: Opals

By Maddy Robinson & Sandra Pimlott FGAA Dip D.T. NCJV Reg Valuer October 31 2019

Opals are one of the most brilliant gemstones, with varying colours and patterns formed by different methods many millions of years ago. A form of hydrated silica, an opal’s colour can range due to the size of the silica spheres, with the larger spheres giving the flashes of red and orange and the smaller giving the colour ranges in the blue green.

Some of the oldest opals in existence are from the Ordovician period, up to 595 million years old. They can be found all around the world in places such as Mexico, Ethopia, North Brazil, Peru, The United States (in Nevada and Idaho), Honduras, Indonesia, Somaliland, Slovakia and of course, Australia. Some of the oldest pieces of jewellery with opals are from Hungary and Brazil as the Australian opal fields were at that time largely undiscovered.

In Australia, opals were first discovered in Queensland in 1872, with the first Australian mines opened in White Cliffs, NSW in 1884. There are many native folklore legends surrounding opal, including the in Dreamtime legend, where the creator came down to earth on a rainbow serpent and wherever he stepped on the Earth, the ground began to sparkle and came alive with the colours of the rainbow.

The Olympic Australis remains to be the largest and most valuable opal to date, found in 1961 in Cooper Pedy, SA.

Being sedimentary, metamorphic or volcanic in origin, there are many types of opal, including:

• Black Opals feature a black or semi-black body with variations and patterns in colour, with harlequin being the most prized pattern. Main deposits are from Lightning Ridge or White Cliffs, NSW and is a sedimentary sandstone/claystone.

• White Opals come from Cooper Pedy, Andamooka and Mintabie in South Australia. White opals are typically the least valuable form of opal, as they generally tend to have less vibrant colour than boulder and black opals.

• Boulder Opal are mined from large ironstone boulders under the ground and are distinguishable by their layer of solid brown ironstone on the back of the stone. Boulder opals are only found in Queensland, with major opal fields in Quilpe and Winton.

• Doublets & Triplets Doublets are man-assembled with plastics and natural opals to imitate the appearance of a solid black opal. By adding a black backing to a slice of opal, the colour can become more vibrant - but are much cheaper than solid black opals as they only contain a sliver of genuine opal.
  • Doublets, as its names suggests, consists of two layers:
    • A black backing. The material of this backing varies from supplier to supplier, usually made of industrial glass, black colourless opal or hard plastic.
    • A sliver of opal. The edges  usually rounded off to give the stone a rounded top, or cabochon cut.
  • Triplets consist of three layers:
    • A black backing as above
    • A sliver of opal.
    • A clear capping in the shape of a dome. This is usually made of glass, quartz, or plastic. The dome can protect the opal, magnify the colour and give a cabochon cut.

Buying guide

Understand what opal you are buying. Here are some tips: 

Buy from a reputable source to ensure you are not buying imitation.

Do your research to ensure you are buying the right stone for you. Some sources sell opals that are advertised incorrectly and end up 

Take your opal jewellery to a jeweller for cleaning.

Home care cleaning projects can hurt your opal, so taking your opal jewellery to a jeweller once a year ensures your stone stays clean and safe. Submerging the wrong kinds of opal, such as doublets or triplets, in water can permanently damage them as water can slip between the layers and degrade the stone. And obviously, do not put your opals in an ultrasonic.

Choose your design carefully.

Opals are a soft stone and require care. The best type of ring setting for an opal is an enclosed setting, such as a bezel setting, in order to protect the stone. Claw settings are not recommended.

Opals are a diverse stone - there’s one to suit every taste and budget. 

When choosing an opal, start by outlining your budget. Chat to a jewellery consultant about what colours you’d like to see in your opal. High quality opals will show more play of colour throughout the stone and have more light dispersion. Opals such as harlequin opals, which show a significant amount of red, are considered the most rare.