There are many different specimens of Opal from around the world but in my humble opinion, the most desirable is the precious gemstones from the Australian Never Never. They are resplendent with colour aka "play of colour" that can be seen from any angle. They are a real delight.
The two main regions in Australia where Opal can be found are: NSW - famous for its black opal & opalised fossils from Lightning Ridge, & White Cliffs. The other South Australia - from the mines of Coober Pedy, Mintabie, Andamooka, with its magnificent iridescent gems.
What is Opal: Opals comprise of a hydrated form of Silica. Its chemical makeup is SiO2•n(H2O): Silicon Dioxide which has a variable amount of water in its formula, (Silica is an abundant compound that forms about 12 percent of the earth's surface, however precious Opal is not common).
Millions of years ago in what once was the great inland Eromanga Sea, that stretched over much of the lower central to eastern areas of Australia, specific geological conditions became favourable to the formation of Opal. Where this great sea lingered over time & seeped through the host rock into crevices, catchments & seams it mixed with seasonal ground waters, evaporating the mineral content, flowing & precipitating into layers of tiny spheres, to create common Opal and in places precious Opal.
This process sometimes replaced organic matter, creating opalised bone, shell, or wood; transforming them into rainbow fossils. Australia is the only place where dinosaur bones have been discovered opalised.
No two Opals are the same.
They contain a riot of colours ranging from short wavelength blues to the longest wavelengths of red. Opal has Silica spheres arranged in an orderly network. The structure of the gemstone has small/medium & large spheres pooled to create a kaleidoscopic prism. The size & geometric packing of the spheres determines the colour and quality of diffracted light. This is seen best when the stone is tilted and moved. However common Opal does not display opalescence, (play of colour).
Opalmania struct Australia from the late19th century. Miners fossicked & worked the Never Never, in the hope of finding the colourful, rare & precious Opal gemstone.
Oftentimes they endured extremely harsh and violent conditions.
Commercial mining started by settlers around 1880, with many of the main mines being "worked out" by the end of the 20th century. White Cliff's was depleted by the1930's, Andamooka by the 1970's, & Mintabie started operations in the 1970s & was exhausted by 1990's. Mining still occurs at these sites but with limited production. Opal material is extracted from the Queensland Opal fields (from Winton to White Cliff's in NSW), & the vast region of the Artisan basin, (fields surrounding Coober Pedy, Mintabie to Andamooka). These fields still produce approximately 90% of the world’s supply of precious Opal.
What's in a name
Opal varieties are given fanciful names like Angelstone, Harelquin, Chinese Letters, Pinfire & Yowah Nut, & are indicative of their attribute's, or regions they are found in. Some of the more commonly known varieties are:
Light or white Opals are identified by their pale body tone or body colour. They are often referred to Milk Opal. Although they were originally found at White Cliffs in NSW, they are mainly mined from Mintabie & Cobber Pedy in South Australia.
Black Opals are rarer than white Opals and can be identified by the background darkness called body tone or body colour. Most black Opals are mined from Lightning Ridge. Black Opal that has bright red flashes within it are extremely rare.
Common Opal is left on its original host rock for added weight, strength, size or used in Doublets or Triplets.
Doublet Opals are constructed with a thin layer of opal gemstone adhered to a backing or host rock.
Boulder Opals also displays the precious gemstone still attached to its host rock, ironstone, but is considered solid Opal.
Triplet Opals are less expensive than Doublets & have been very popular in the tourist market for many years. They are made up of a sliver of Opal sandwiched between a backing & a synthetic top.
Taking Care of Opals
Opal have a high-water content & can be affected by sudden heat changes, hard knocks, undue pressure, & chemicals.
Take care to not place them into water or water with detergent, or cleaning products as these may compromise the glue or the construction of a Triplet or Double, or cause a solid Opal to become brittle over time.
Opals are really great for high days & holidays, reserving them gentle outings and formal gatherings creates a real sense of discernment.
Opal Birthstone & Wedding Anniversary
Opals are the gemstone for October, and if you lucky enough after 14 years of marriage, you might be gifted one of these beautiful gems to mark your anniversary.
If you are looking for a jewel that is something a little different, that can be bold or be understated elegance then Opals really work a treat. At Minturn Jewellery, we have a selection of solid white Opal with good play of colour, different Doublet & Triplet Opals, & we have a fabulous New Zealand Supplier who can source a very special piece of precious Opal to suit your taste & budget. Get in touch, we are happy to help.
For further reading & gemological information pop onto Mindat to view their information.