“In precious opals, there might be a dash of red here, a seductive swirl of blue there, and in the centre, perhaps, a flirtatious glance of green. But each stone flickers with a unique fire and a good opal is one with an opinion of its own” – Victoria Finlay, British writer and journalist.
This quote beautifully captures the essence of the opal. While it may be world-renowned, few people are aware of its origin and the reason behind its glittering hues.
So today, we’re going to discuss the opal’s formation at length and answer some commonly asked questions.
Keep reading…
What Is An Opal?
It is a semi-precious gem that’s prized for its ‘play-of-colour’, which refers to the display of various patterns and hues on the surface of the opal in reaction to a light source.
In terms of colour, black is the rarest while white is the most common. But you can find opal in various other hues, including red, orange, blue, pink and brown, among others.
How Is It Formed?
The opal is a hydrated amorphous form of silica. Its water content can range from 3% to 21% in weight. This is why it is categorized as a mineraloid, and not a mineral.
In Short…
The gemstone is formed through the hardening of silica gel present in the cracks of sedimentary rocks.
The Longer Answer
Opals are created from a combination of water and silicon dioxide. Due to weathering, the sedimentary rocks (usually sandstone and mudstone) release silica into the groundwater.
As the water continues to flow through the cracks and crevices of the rocks, it carries the silica with it. Eventually, this silica-rich solution gets trapped between the sandstone and the underlying rocks which causes it to convert into a hardened gel, once the water evaporates. Over a period of time, this gel eventually turns into an opal.
Their ‘play-of-colour’ is created through the diffraction of light caused by the silicon spheres that act as prisms. Depending on how the structure is formed, the light can deflect in multiple ways to create various colours.
The variation in the stone’s appearance is caused due to a multitude of reasons such as the climate, along with the rise and fall of the water table, among others.
How Are They Mined?
Mining is conducted through the process of shaft sinking, typically with a pick and shovel. Here, the shaft is sunk until it reaches the ‘opal dirt’. Once that is achieved, the miners expand sideways and begin searching for the stones; any opal found is then gently extracted.
It’s interesting to note that many of the opals found during excavation are not considered precious. This is because they lack the play-of-colour that this gem is famed for.
How Are Opals Treated?
Opals are usually treated to improve their appearance and durability. The two most common treatments are as follows:
1. Sugar Method
During this treatment, the jewel is submerged twice; first in a sugar solution and then in strong sulfuric acid. This intensifies the visibility of the colour flashes.
2. Smoke Method
Here, the gemstone is wrapped in paper before being exposed to smoke and fire. The soot particles penetrate the surface of the stone and darken the background so that the flashes of colours are more prominent.
Conclusion
Opals are one of the most unique gemstones in the world, with no two pieces being 100% identical. So, if you’re looking for a jewel that is beautiful yet different, then this one certainly fits the bill. What’s more, with a variety of beautiful opal rings, opal earrings, opal bracelets and opal necklaces available in the market today, you are sure to find a piece that suits your preference and style.
