Opal is the birthstone for October and is also a suggested gift for celebrating a 14th wedding anniversary.
The name Opal takes it origins from the Sanskrit word Upala meaning jewel.
There are two types of Opal, the Common and the Precious Opal. Precious opals display play of colour, a unique flashing of light into rainbow colours. This is created from sub-microscopic spheres that are stacked in a grid like pattern. Lightwaves that travel between the spheres diffract or bend creating the rainbow of spectral colours. Common opals do not display a play of colour.
Opal is the product of seasonal rains that drenched dry ground in regions such as Australia’s outback. The showers soaked deep into underground rock carrying dissolved silica, a compound of silicon and oxygen, downward. During dry periods much of the water evaporated leaving solid deposits of silica in the cracks and between layers of sedimentary rock. The silica deposits form the opal.
Whilst there are many different categories of opals experts divide opals into five main categories:
White or light opal – these are translucent to semi translucent with a play of colour against a white or light grey background. This is the most common type of opal.
Black opal – translucent to opaque with a play of colour against a black or a dark background
Fire opal – Transparent to translucent with brown, yellow, orange or a red body colour. Fire opals do not often show any play of colour
Boulder opal – translucent to opaque with a play of colour against a light to dark background, Fragments called matrix from surrounding rock become part of the finished gemstone.
Crystal/Water opal – transparent to semi-transparent with a clear background. This type of opal shows an exceptional level of play of colour.
The majority of opal supplies today primarily come from Australia, Mexico and the United States. Most opals are cut in a rounded cabouchon to enhance the play of colour.
Opal should be treated with some care. It is softer than many other gemstones and has a hardness of 6 on the Moh’s scale. It should be stored carefully to avoid being scratched by other jewellery, and should be protected from knocks on any exposed corner of the stone to avoid chipping. Opals do not like exposure to heat or acid. They can be cleaned gently using warm, soapy water and a soft brush. Avoid using ultrasonic or chemical cleaners.