Opal

Formation of Opal

Light of the World, Pandora, Queen of Gems – or more commonly, opal is a strongly hydrated form of silica characterised by its amorphous structure. This luminous gem occurs in the fissures and layers of underground sedimentary rocks and is a by-product of floods and heavy rains that cause water to filter through the ground, leaving deposits of silica behind. Although opal can form in the cracks of nearly every rock, it is most commonly found in basalt, sandstone, marl, rhyolite and limonite. Depending on the location and circumstances in which opal formed, the stone can be either transparent, translucent or opaque, with white, black or polychromatic background. Majority of the gems are either white, grey or green, while the black opal is considered to be the rarest.

Play of Colour

There are two categories of opals: precious and common. Most people are more familiar with precious opal and its characteristic unique display of sparkling rainbow hues. This particular attribute is known as ‘play-of-colour’ and its cause lies in opal’s distinctive microscopic structure. Although opal is a mineraloid that does not demonstrate crystallinity, it is composed of silica nanospheres tightly arranged in a cubic or hexagonal grid-like pattern. Such structure causes diffraction and interference of the light waves penetrating it, breaking them up into sets of spectral colours visible to the naked eye.

Common Opal

Common opal, otherwise known as ‘potch’ is an opaque and milky variety of opal that does not manifest the play-of-colour seen in precious opals. Instead, the potch displays a delicate opalescent sheen across a wide range of colours it comes in.

The National Gem of Australia

First opals were discovered during Roman times in the region covering modern Czechia and Slovakia. The area was an active producer of the gemstone until the early twentieth century. In 1887, expansive deposits were found in Australia; the country remains the main source of opal to this day, delivering approximately 95% of global demand. The world’s largest gem-quality opal, the ‘Olympic Australis’ was also found in the Land Down Under. Unsurprisingly, opal is considered as Australia’s national gemstone. There are a few other localities in which the iridescent gem can be found – these are in Ethiopia, Mexico and parts of the United States.

Supernatural Powers

The unique appearance of opal has been a source of legends and superstitions since pretty much its discovery, with numerous cultures attributing supernatural powers to the stone. According to the ancient Arabs, opals were actually fragments of lightning that fell from the sky during a thunderstorm. Early Greeks believed that opal could prevent disease and bestow its owner with the ability to predict the future. The Romans marvelled at the kaleidoscopic colours of the stone, considering it as the most precious and powerful gem in existence, the only one suitable to be presented as an offering to the Gods.

Gift for Cleopatra

The veneration in which opal was kept by the Ancients is perhaps best illustrated by a story about wealthy Roman senator Lucius Nonius Asprenas, who is said to be the owner of one of the finest opals ever known. The spectacular gemstone caught the eye of Mark Anthony, who wanted to acquire it for his beloved Cleopatra, Queen of Egypt. Nonius Asprenas was unwilling to part with his treasure, choosing exile from Rome over handing the stone to the Roman general.

Admired for Ages

After a short period of decrease in popularity caused by superstitions associating opals with bad luck, the colourful gem returned in all its glory, embellishing Victorian and Art Nouveau jewellery. Queen Victoria adored opals – so much that in 1853 her husband, Prince Albert designed an intricate opal tiara to be made for his beloved by the House of Garrard. Fascination with opals continued through the twentieth century – from Andy Warhol’s 1977 ‘Opal the Rainbow Gem’ exhibition, through Elvis Presley’s signets, to Elizabeth Taylor’s collection of opalescent jewels. Even today, with an abundance of the finest gemstones available on the market, opal still enthrals and captures people’s imagination.