Opal – Your Complete Guide
With their unique and breathtaking beauty, opal gemstones have been revered for thousands of years. Until the discovery of enormous quantities of opal in Australia during the 1800s, the only other known source of opal was Červenica, a small village in southern Slovakia.
Precious versus Common Opals
Opal is classed as a sedimentary mineral and its crystalline structure is comprised of anywhere between three and twenty-one percent water. Opal worthy of use in jewellery and gemstone ornaments, will typically contain between six and 10 percent water. Under the right geophysical conditions, water filters beneath the earth, providing it with an abundance of dissolved silicates.
Upon entering a subterranean chamber, the water releases the silicates in the form of tiny spheres, which go on to evolve into opals. If these spherical droplets of silicate possess the same physical dimensions and are precisely piled on top of each other, they diffract light. These constitute precious opals. On the other hand, if the silicate is irregular and not randomly dispersed, then the result will be common opals.
Facts About Opal
- There are currently 25 known varieties of opal
- There are two primary categories of opal: precious and common
- It’s available in many different colours, including white, orange, blue, red and violet, to name a few
- There are currently over a dozen different definitions used to describe the pattern of a particular opal specimen, including Chinese writing (where the distinct pattern is reminiscent of Chinese characters), Flame (self-explanatory), Windmill, Floral and Fern Leaf
- It’s quite delicate and damages prone, with a Mohs hardness rating of 5.5 to 6.5, meaning that extra care must be taken when wearing opal jewellery
- Samples can either be highly transparent or opaque
- It’s the birthstone of October
A Kaleidoscope of Colours
Opal’s most famous and wondrous quality is its ‘fire’, which is an industry term describing its ‘play of colours’. A direct result of diffraction of light. The specific colours displayed by an individual opal, are determined by the size of the silicate spheres present within its structure and by the angle at which the gemstone is observed.
Artificial opals often exhibit rich colours, typically in a mosaic arrangement. With the use of a magnifying glass, it’s easy to identify a pattern that almost looks like a reptile’s skin. Other times, the structure may resemble a wire mesh.
Fake opals are noticeably soft and can be pierced with the point of a needle. Fake opal comprised of glass, possess glass droplets and distinct twirl patterns.
Opal Enhancement Techniques
Oil, Plastic or Wax – helps to enhance fire quality. Helps to conceal any cracks present within the structure. Infusion of oil or wax generally results in reduced structural stability. Meaning that even greater care must be taken to prevent damage. Plastic infusion can often only be achieved with the aid of specialised lab equipment.
Black Plastic – creates the impression of black opal. Helps to conceal any cracks present within the structure. Samples subjected to this treatment are often stable following the process. Can generally only be performed with specialist equipment. Evidence of this treatment is able to be identified, as Specific Gravity (SG) value becomes lower than what is typical for naturally occurring black opal.
Opal deposits are found in countries right around the world, with Australia being home to 95-97% of all precious opals. Other sources of opal include Brazil, Slovakia, Ethiopia, Tanzania, the United States and many more.
How to Clean Your Opal Jewellery
Opals are quite fragile but when looked after properly, can be suitable for jewellery wear. They’re particularly vulnerable to damage from temperature change, which causes the stones to develop noticeable cracks. Also, if opal becomes scratched and tarnished, It’s not uncommon for it’s spectacular colour to disappear entirely, leaving a sickly pallid hue. Thankfully, a careful polish will typically resolve this and restore its vibrancy.
With a hardness rating between 5.5 and 6.5 on the Moh 10 point scale, opal can easily be damaged beyond recovery. Due to the ease at which it can be scratched, opal jewellery is better worn as earrings or as a necklace. Owners of opal jewellery must never clean their jewellery using ultrasonic cleaners, by boiling or by steaming. Instead, clean them using luke warm, soapy water and a soft-bristled brush. If you need additional advice on looking after your alexandrite jewellery, consult your local jeweller.
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