Opal marks the official birthstone for October. They have always been associated with passion and love.
Opal is a hydrated amorphous (meaning it does not have a crystal structure) form of silica. Its water content is usually between 6 and 10%. It forms at a relatively low temperature and may occur in the fissures of almost any kind of rock, most commonly found with limonite, sandstone, rhyolite, marl and basalt.
The transparency of opal depends on the conditions in which it formed, the background colour may be white, black or nearly any colour of the visual spectrum. Black opal is considered to be the rarest, whereas white, grey and green are the most common.
Opal occurs in more than twenty other countries, including Zambia, Ethiopia, Guatemala, Poland, Peru, Canada, New Zealand, Indonesia, the USA, Brazil, and Mexico. The country producing the finest quality of Opal is Australia.
Opals are broadly classified in two categories – precious opal and common opal. Precious opal displays play-of-colour, common opal does not. Play-of-colour is defined as “a pseudochromatic optical effect resulting in flashes of coloured light from certain minerals, as they are turned in white light.”
For gemstone use, most opal is cut and polished to form a cabochon. “Solid” opal refers to polished stones consisting wholly of precious opal. Opals too thin to produce a “solid” may be combined with other materials to form doublets and triplets.
Fire opal is a transparent to translucent opal, with warm body colours of yellow to orange to red. Fire opals that do not show play of colour are sometimes referred to as jelly opals.
In the Middle Ages, the opal was known as the “eye stone” due to a belief that it was vital to good eyesight. Blonde women were known to wear necklaces of opal in order to protect their hair from losing its colour. Some cultures
thought the effect of the opal on sight could render the wearer invisible.
In the late 18th and early 19th centuries, opal began to fall out of favour in Europe and was associated with ‘bad luck’. Queen Victoria’s favourite gemstone was in fact the opal and she continued to wear opals throughout her reign. Many Australian opal fields were discovered and worked during Victoria’s long reign.
How to care for your opal jewellery:
- Clean them using warm soapy water and a soft brush.
- Avoid ultrasonic cleaners and chemical cleaners.
- Avoid getting opal doublet jewellery wet as the thin film of glue bonding the layer of opal to the backing is prone to breaking down, causing the doublets to break.
- Opal is a soft material, 5. 5 – 6 . 5 on the Mohs’ scale of hardness, therefore it can be scratched by dirt particles. Opals can also crack if knocked.
- Opals do not like heavy exposure to bright sunlight or heat as this can cause them to crack.
- Do not clean opal jewellery in an ultra sound.