When we think of opals, our thoughts wander immediately to Australia. It which remains the benchmark for countries of these magnificent stones; despite competition from Mexico with Fire Opal and Ethiopia with its fabulous Welo Opal (I also invite you to read or reread my earlier article on these Ethiopian Opals). For now, let’s take a look at the land of kangaroos, rugby, surfers and of course … Opals!
Origin of Boulder Opals
The Boulder Opal, comes from the state of Queensland in Australia, more specifically in the regions of south-western Queensland Quilpie, Yowah, Eromanga. The sedimentary rocks of this region date back to the Cretaceous period. Thus, the rock comes from the period that began around 145 million years ago, with the end of the Jurassic period, and ended around 66 million years ago, with the start of the Paleogene period.
Most opals come from very arid areas and during periods of heavy rainfall, tiny particles of silica were dissolved in water. The constant change of moisture and subsequent evaporation led to strengthening of the silica and thus the beautiful Opal.
The first Boulder Opals were discovered in 1869 and the first mine was created in 1871 in Quilpie. Miners started to arrive very quickly after it was opened to tap the newfound riches of the region. These miners included Bekerlman and Lambert, who presented Opals at the ‘London Gem Exhibition’ in 1893 where they were an immediate sensation.
If the Black Opal remains the most popular Opal in Australia, the Boulder Opal is definitely second. It represents only 2% of the production of Australian Opal. Its production is expected to increase however as the regions where Boulder Opal is found extend over very large areas, but much of this is still yet to be explored.
Characteristics of Boulder Opal.
Boulder Opal is found in iron ore, it fills veins, crevices and cracks. This bedrock remains in opals once they have been cut, hence the name. Cutting these gems is therefore a delicate matter, attempting to contrast the hardness of the iron ore against the hardness of the opal. But thanks to this feature, these opals are known to be stronger than their counterparts. The Boulder Opal is particularly interesting because the contrast of the black rock and the colour matrix especially highlights the play of colour in this Opal. For Boulders Opals, its play of colour normally occurs in blue-green tones.
They are usually cut in the direction of the grain of Opal with iron ore ‘bedrock’ supported on the bottom, the stone surface is then covered with Opal. Sometimes, the cut is also perpendicular to highlight the silica stripes trapped in the rock.
These stones bring joy to jewellery designers such as Irene Neuwirth. She has made superb earrings featuring boulder opals which have been elegantly worn by Octavia Spencer at the Golden Globes, Busy Philips, Star of “ER”, “How i meet your Mother”, “What think men “or by the dancer Jenna Dewan-Tatum, known for her leading role in” Step Up. “ Jennifer Hudson also adorned Boulder Opal hoop earrings on the red carpet at the 2013 Oscars ceremony.