There are different varieties of the Opal: the Precious Opal which displays flashes of colour (iridescence) and Common Opal which is opaque with no iridescence.
95% of the world's opals are sourced in Australia, and most of the precious black opals actually never leave the country. The stone is normally found in cavities in sedimentary rocks and in veins of igneous rocks.
An opal is hardened silica gel, which usually contains between 5-10% water. Due to this water content, opals can often crack from loss of water. To prevent this happening, treatment in the form of oiling can be applied to help seal the stone. This procedure is not permanent but can be repeated and helps keep the stone looking its best.
In the Middle Ages, opals were believed to possess all virtues of each gemstone whose colour was seen in the colour spectrum of the opals, and in turn the stones were considered to provide great luck and fortune.
Fire Opals are slightly different to the Precious and Common Opals. They are generally one bright colour, usually from yellow to red, and are very clear and transparent. These are mainly found in Southern Mexico. It has been said that these stones look like boiled sweets!
We have a range of opal jewellery in our St Albans store to see for yourself.