Opals are unique gemstones that display dazzling play of colour mixed with brightness, shimmer and sparkle. These semi-precious gems have adorned men since the dawn of history. Being regarded as one of the most beautiful stones, opals are must-have gems for many jewellery lovers.
Opal Origin and Formation
The name “Opal” comes from the Sanskrit word Upala which means “precious stone”. These beautiful gems have been valued since ancient times. People were crafting jewellery from opals thousands of years before the pyramids of Egypt were built.
A remarkable discovery made by the famous anthropologist Louis Leakey in 1939, showed that opal artefacts found in the cave of Kenya dated back to 4000 BC, more than 6000 years ago.
Judging by the discovery, Ethiopia was probably the earliest source of these gemstones. However, the main source for the ancient world was Eastern Europe and Turkey.
Opals were exceptionally rare gemstones until 1800 when they were discovered in Mexico and Australia, the latter still remains the main source, making 95% of all opals mined.
There is still an argument over how opals were formed. Most scientists follow the belief that opals are formed by water seeping into cracks in various rocks. When the water evaporates away it leaves silica gel-like substance which then hardens and turns into opals.
Describing the colour of opals is not an easy task since they display all the colours of the rainbow in one abstract painting.
To make things easier, let’s start with the basics. There are two types of opals, precious and common, precious opals display play of colours, while commons do not.
Precious opals are further divided into three main categories: White Opals, the most common type, Black Opals, stones that show colours against a dark background, and Fire Opals, which mainly display bright yellow, orange or red colour.
There are two elements that help opals get their colour: background colour, which is created by impurities within the gemstone and “play of colour”, which is produced by silica structure of the gem.
Opals are “filled” with millions of tiny spheres of hard silica sitting on top of each other. When light hits these spheres and bounces off at different angles and directions the magic happens and opals show unique dazzling light.
Opals come in such an array of colors, that determining the rarest and most valuable colour is not that easy. However, red is thought to be the rarest and the most valuable colour because red spheres within an opal are less common. If you add red colouring to the rare black background, you get the most prizes opal gemstones.
Opals have many patterns. In fact, you can never find two opals that have the same pattern.
The most valued and sought after pattern is called Harlequin, which shows large sections of colour which are nearly the same size and shape like a mosaic.
Other remarkable patterns are:
- Flagstone – large sections of colour with a random pattern;
- Straw – random ribbons of overlapping colours;
- Chinese Writing – thin stips of overlapping colours that look like Chinese characters;
- Pinfire – dots or flecks of colour;
- Floral – a pattern that looks like a flower;
- Broad Flash – large sections of colour that flash as you turn the stone.
As mentioned above there are two types of opals, precious and common. Precious opals are further divided up.
Black or Dark Opals are the rarest and most expensive. The term black refers to the background colour, which can be completely black or just of a dark tone. These opals are mostly found in Ethiopia and Australia.
White or Light Opals are the most common variety. Although they have a white, milky or transparent background, this variety still displays a stunning play of colour.
Fire Opals are the stones that have a yellow, orange or red colour. These gems have bright colour but usually, do not display eye-catching play of colour. If they do, it’s generally deep within the stone. Such rare gems are called Precious Fire Opals or Jelly Opals.
Boulder Opals come in a wide range of colours. Such opals are still attached to the rock on which they are formed. The background rock gives a unique beauty to the opal and dark ones are the most popular.
Matrix Opals are really intriguing. This variety displays flecks of opals ingrained into little pores or holes found in rocks.
In general, there are over 20 widely known varieties of opals, which get their names after their country of origin or their colour, size, patterns and natural designs.
As we know clarity is the degree of transparency or lack of blemishes in a gemstone. Opals are special stones and differ from these rules. They are graded as transparent, translucent or opaque.
With black opals, clarity is not an issue, since they should have an opaque background on which to show off the colours. However, with crystal opals, we need as high clarity as possible to see the play of colour. Cloudy or milky opals are certainly valued less.
With Boulder and Matrix Opals clarity is not an issue as well since opal material itself is included in another rock.