Spectacular and opulent, Opal encapsulates all of nature’s splendour: fire, lighting, all colours of the rainbow and of the gentle sparkle of the seas. A single stone may flash every colour of the spectrum with astounding intensity and quality of colour. Writing in 75 AD, the famed Roman scholar Pliny the Elder observed that “Some opali carry such a play within them that they equal the deepest and richest colours of painters. Others… simulate the flaming fire of burning sulphur and even the bright blaze of burning oil.” He marvelled at this kaleidoscopic gem which could encompass the red of a Ruby, the yellow of a Topaz, the blue of a Sapphire, the green of an Emerald, the purple of an Amethyst and the fire of a Diamond.

What is Opal?
Stunning Opal formed thanks to seasonal rains drenching the arid ground, seeping deep into ancient underground rock and carrying a gelatinous compound of silicon and oxygen (dissolved silica) with it. During drier periods, most of the water would evaporate, leaving deposits of silica between the layers, within the fractures and in the veins of the sedimentary rock. These deposits would solidify and form gorgeous Opal stones. In rare circumstances Opal became replacement material in fossils, or formed as stalagmites or in masses exhibiting botryoidal growth (a globular external form resembling a bunch of grapes).

Opal is amorphous and has neither a definite chemical composition nor a crystalline structure; it is therefore considered a ‘mineraloid’, rather than a mineral. Its unique structure consists of sub-microscopic silica spheres forming a pyramid-shaped grid, interspersed with water and additional silica. Even after solidifying, Opals maintain a water content ranging from 3% to 21% (usually 6% to 10%). 

Characteristics of Opal
Opal is characterised by mesmerising displays of ‘opalescence’ or ‘play of colour’. These are two different effects of the scattering of light within the stone’s microcrystalline layers, due to the refraction of light entering the gem and hitting or passing through the stone’s structure. As the light travels between the silica spheres, the light waves diffract, bend or even blend producing a gorgeous iridescent display.

In Opal gems in which the microcrystalline silica spheres are more randomly arranged, the effect of the above mentioned light diffraction will be a pearly or milky lustre known as ‘opalescence’, which is a subtle iridescence in the form of soft colorations or white haziness. This effect occurs in what is known as ‘Common Opal’ or ‘Potch’.

In rarer gems, in which the sub-microscopic spheres are stacked in more orderly grid-like patterns, the refraction of light will exit the gem displaying the whole spectrum of the colours of the rainbow, thus resulting in a ‘play of colour’. This play of colour may consist of large flashes of colour (known as ‘schillers’) or tiny dense flashes. The size of the spheres and their geometric packing will determine the colour, quality and intensity of the colour flashes, which in turn are a determining factor in the value of an Opal stone. Play of colour occurs in what is known as ‘Precious Opal’, which is rarer than Common Opal and found in a limited number of locations worldwide.

A further characteristic of Opal is its hardness: It measures about 5.5 to 6.0 on the Mohs hardness scale, which means it’s a relatively soft stone which can easily chip or scratch. This makes it a wonderful stone for earrings, brooches, pendants and in general pieces which are less likely to be subjected to impact or abrasion. When used for pieces such as rings it is best to set Opal in frames such as a bezel, which will protect the stone, rather than placing it in a prong setting, which will allow the edges of the gem to be exposed.

The origins of its name
The name ‘Opal’ comes from the Latin ‘opalus’, which is believed to originate from the Sanskrit ‘upala’, meaning ‘precious stone’. The name ‘opalus’ in the Middle Ages evolved into ‘ophthalamos’ or ‘ophthalamius’, meaning ‘pertaining to the eye’. While in Greek the same gem was called ‘opallios’, meaning ‘to see a change in colour’.

Types of Opal
Opal is divided in two main classes: Precious and Common. As mentioned above, Precious Opal is the rarer type and displays ‘play of colour’, a phenomenon by which it flashes magnificent iridescent colours when viewed from different angles or when the light source is moved. Precious Opal is highly sought after and its desirability is based upon colour intensity, uniformity, diversity, pattern and the ability to be seen from any angle.

Common Opal instead, is found in more abundance and in a greater number of locations throughout the world. It does not exhibit play of colour and does not, therefore, attract the same interest by collectors. However, Common Opal is very often colourful, attractive and lustrous, and can be cut into gorgeous high polish gems.

Opal comes in an abundance of different varieties with an endless range of wonderful names used to communicated about them. Some of these names are universally accepted while some are employed by individual dealers to describe specific characteristics of the stones they trade. Some of the varieties are named according to their colour, while other names describe the stone’s fire pattern, place of origin or reference the Opal-host rock relationship. Below is but a handful of these varieties and is by no means an exhaustive list.

Black Opal is one of the most popular and valuable varieties of this stone. It has a black, dark grey, dark green or dark blue background and displays a bright play of colour. Almost all of the world’s supply of Black Opal is mined in New South Wales, Australia. As a consequence, in 2008, this was officially proclaimed the official gemstone of said state. 

Crystal Opal is a transparent to translucent Opal stone with play of colour.

Ethiopian Opal is a hydrophane Opal (a form of Opal which is capable of absorbing water), and forms in the seams between layers of volcanic ash. In fact, while all Australian Opals are of sedimentary origin, Ethiopian Opals find their origins in volcanic activity. They come in a variety of tonalities and usually display amazing flashes of colour. The original Ethiopian Opal was discovered on the Yita Ridge in 1994 and is prone to cracking when it absorbs water. A more recent discovery in the Welo District in 2008 unearthed a new gem quality which is incredibly stable despite its porosity: it absorbs water, changes transparency or opacity and then reverts back to its original state with no cracking or other adverse reaction.

Fire Opal is a gorgeous transparent to translucent stone with a warm, fire-like background colour. This variety is defined by its colour: shades of red, orange or yellow. It does not usually show a play of colour, though stones will occasionally exhibit bright green flashes. This type of Opal is mostly found in Querètaro, Mexico.

Girasol Opal, sometimes referred to as Water Opal is a type of Hyalite Opal (this is a type of Opal with a clear, glassy appearance) which presents a bluish glow or sheen that follows the light source around. This effect is not the product of play of colour as in Precious Opal, rather it is due to miniscule inclusions. The main locations in which this type of Opal is found are Mexico and the United States (more specifically, in the state of Oregon).

Harlequin Opal is a variety in which the play of colour  is displayed in a consistent diamond-shaped or rectangular pattern and is usually tremendously vivid. This is one of the rarest and sought after varieties of Opal. 

Matrix Opal is the term used to indicate gems in which Precious Opal and the host rock (ferruginous sandstone or ironstone) are intricately intertwined. The Opal occurs as an infilling of pore spaces within the rock or as a network of veins, it may even be nestled between the grains of the parent rock. This is also known as ‘Type 3 Opal’.

Yellow Opal is a bright and gorgeous variety, this may be translucent or opaque. The translucent stones are usually cut and polished into faceted gems, while opaque ones are cut into cabochons or are simply tumbled and polished.

Where can Opal be found?
About 97% of the world’s supply of Precious Opals comes from Australia, with the state of South Australia accounting for an overwhelming 80%. Australian Opal is now famous across the world for its brilliant tints and marvellous play of colours. It was discovered in 1849 and by the end of the 19th century it began dominating the world’s supply. It is mostly sourced from a handful of mining areas including Coober Pedy (discovered in 1915), Lightning Ridge (1902), White Cliffs (1890), Andamooka (1930), Mintabie (1931) and the Queensland Boulder Opal Fields centring around the town of Quilpie (perhaps one of the oldest mining mines discovered in 1869).
Apart from Australia, other Opal sources include Ethiopia, Brazil, Mexico, Tanzania, Peru and the United States.
In 2008, NASA's Mars Reconnaissance Orbiter discovered a number of Opal deposits on Mars. Satellite images show that the ground is in areas covered with hydrated silica rock debris while researchers also observed layers of Opal exposed in the outcrops of crater walls. As the formation of Opal requires water (it consists of hydrated silica), this is a significant discovery because it is yet another evidence that water was once present on Mars. 

World famous Opal masterpieces
Nessie – a two meter long opalized pliosaur from Australia. The Opal filled the empty spaces left in the fossil bearing rock by the bones dissolved by acidic ground water. Nessie is currently on display at the National Opal Collection in Sydney, Australia.

Sun God Opal – a 35 carat Precious White Opal carved in the shape of a human face and set in a gold frame resembling rays of sun. This is a  mysterious piece, said to have been mined and carved in Mexico in the 16th century and displayed in a Persian temple for several centuries before being bought by the Hope Family. This piece is currently on display at the Chicago’s Field Museum of Natural History.

Dark Jubilee Opal – a 314.4 carat free-form polished Black Opal. It came from a mine in Coober Pedy, Australia and is currently on display at the Smithsonian Institution in the United Sates.

Peacock Brooch –  a decadent piece of jewellery designed by Harry Winston. It features a magnificent 32 carat Black Opal (found in Lightening Ridge, Australia) which forms the body of the peacock, the sumptuous tail is made of yellow gold accented with Sapphires, Emeralds, Rubies and Diamonds, while the head and neck are set with Sapphires and Diamonds. The brooch is now on display at the Smithsonian National Museum of Natural History in the United States.

Tiffany Necklace – a wonderful example of Art Nouveau jewellery designed by Louis Comfort Tiffany sometime between 1915 and 1925. This is a stunning Black Opal and Demantoid Garnet necklace, the Black Opals are from Lighting Ridge in Australia while the brilliant green Demantoid Garnets are from Russia.

Olympic Australis Opal rough – an extraordinary and unique Opal weighing an astounding  17,000 carats (7.6lbs!), this is reportedly the largest and most valuable Opal gem ever found. It is 11 inches long, 4 ¾ inches high and  4 ½ inches wide and was found in 1956 at the Eight Mile opal field in Coober Pedy, South Australia.

Properties of Opal
Just as Opal stones absorb and reflect light, they also pick up on feelings, thoughts, buried emotions and desires. These are amplified and returned to the source, helping one’s traits and characteristics surface for examination and transformation. This process will highlight positive thoughts, actions and emotions, enhancing the positive and helping foster one’s potential. Nevertheless, it will also magnify one’s negative attributes and actions, a process which may prove to be uncomfortable for some. However, this will enable one to understand how destructive negative emotions can be and consequently begin a process of letting them go. 

Emotionally, Opal if often used to promote a sense of calm and security, helping ease stress and depression. This stone can help placate restless thoughts and racing minds which dwell on the past or anticipate the future. It also helps hold back excessive brooding, so that energies and efforts can be redirected to bettering one’s thoughts and actions. Furthermore, Opal stones draw on the energy deriving from the water within them to enhance one’s self esteem and a sense of self worth, enkindling enthusiasm and optimism while at the same time releasing damaging inhibitions which can hold us back.

Opals are known to help centre the mind and stimulate happy dreams. They are particularly soothing gems for children who have a tendency to sleep badly or have inexplicable recurring nightmares. These gems can also be of help when a child has an invisible or imaginary friend with whom they have a negative or destructive relationship. More generally, this is a soothing stone which can be used to calm turbulent emotions and inspire a sense of hope and inner peace.

Esoteric Opal
Opal stones come in an endless array of colours and every dominant colour may be utilised to stimulate different chakras. As an Opal may present brilliantly iridescent plays of colour, one stone may also activate several chakras at once creating a more direct connection between them and the Crown Chakra (also known as the Seventh Chakra).

This mesmerising and seductive stone is also known for opening the Heart Chakra (also known as the Fourth Chakra), inspiring love, renewal and fidelity. This relates to any kind of love, from the gentle and unconditional , to the fiery and sensual, to the passionate and erotic, and any shade of love in between these. Opals can be used to intensify feelings and release inhibitions; they should however be used with caution as these stones can also diffract and scatter energy. Therefore, when used to amplify or explore feelings, other gemstones should be kept at hand to aid integration and support one’s centring. 

The wonderful spectrum of colours in Opals is also known to heal the aura. The stone in fact acts as a prism, irradiating the aura with light and colours, drawing energy to it which will sooth and clear emotions, and enhance one’s love for life. 

Furthermore, this is a stone of inspiration, meaning it has the power to enhance one’s creativity and imagination. It is thought that such energy derives from the spirit of Opal, whose dashing colours at times mimic the spirit of a child who spontaneously plays whenever and wherever he or she pleases; this imaginative spontaneity is carried into the realm of our life inspiring creativity and joie de vivre.
In the spiritual or psychic realm, Opal is known to enhance one’s cosmic consciousness and stimulate insight. It can help enhance feelings, thoughts and intuition and can be used in daily life as much as in astral journeys as a protective stone. Its energy vibrations are used for protection in meditation and inner-work as well as when venturing in ‘dangerous’ spaces, such as to keep safe during dream-work or shamanic journeys, in which stealth and care are required. 
Opal is also used as a protective stone to shield oneself from other people’s negative thoughts and energies, preventing their absorption. Just as the stone’s structure creates diffraction (interfering with light rays and thus producing iridescent colours), it also creates helpful interference in challenging situations which threaten one’s feelings or mood. Furthermore, Opals are said to provide a ‘cloak of invisibility’ in situations in which one would like to fade in the background and not be noticed.
This is a wonderful stone to have during times of transformation. Due to its higher concentration of water than most stones, Opal is considered a Water stone; just like water flows over the rocks and roots it comes across along its course, the energy of this stone can help one continue on their path regardless of challenges and obstacles. When embarking on a journey of transformation, Opal is an invaluable stone to hold close to the heart.
Opals are stones strongly connected to motherhood. These stones make exceptional gifts for new mothers and mothers-to-be as they resonate with the energies associated to the Mother Goddess. Also, if buried under a willow or any fruit tree at full moon, a Milk Opal stone is known to aid conception. Any variety of Opal can provide powerful emotional support for mothers-to-be, helping overcome fears of childbirth and also alleviating common fears relating to the pregnancy and to the early months of the new baby’s life.