Black Opal jewelry is some of the most sought after gemstone jewelry in the world, being fifth after diamonds, sapphires, rubies and emeralds. This is because opals are some of the most beautiful gemstones available. And whilst most people have probably heard of black, white and fire opals, boulder opals are probably less well known. So why are they becoming so popular?
The body colors of these gemstones are derived from the host rock in which they formed and are categorised as black, gray, white, fire, crystal or jelly. Despite this, opals actually exhibit a wide variety of colors, including pink, fiery orange, tropical blue and others. However, they are most prized for their internal play of color and fiery opalescence. In a good gemstone, the effect is like the rainbow display on the surface of a soap bubble.
Opals have a unique physical structure. They are comprised of silicon dioxide, which is also the major component of sand. However, in opal, the silicon dioxide forms minute spheres which aggregate into a pyramid shaped grid. And tiny droplets of water become trapped within this grid as the opal forms. The pay of color seen within an opal comes from fractures and faults within this pyramid structure. And whilst this is the same for all opals, not all opals are the same.
So what exactly is a boulder opal?
Like 95% of opals used in jewelry worldwide, boulder opals are found in Australia. However, rather than being mined in the conventional way, these specific opals are found thinly spread over a extensive region of Australian Ironstone, also known as boulder country. In the natural state, the gemstone forms to fill in the cracks and crevices of the Ironstone boulders.
Unlike black, fire, white and grey opals which are readily cut from their host rock, opals in ironstone boulders are so closely associated with it, and sometimes for such thin tracks as they fill in the crack in the rocks that they cannot easily be cut from their host rock. This was initially a stumbling block which prevented these gorgeous gems from taking their rightful place in opal jewelry.
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