Opals are beautiful, colorful, and precious in more ways than one. They also come from all over the world, with the majority of stones coming out of Australia, followed by Ethiopia. Even though all opals have the same general chemical framework, the origin of the stone matters. At Automic Gold, we only use ethically mined Australian opals for our jewelry because they are non-porous, can get wet, and are stronger than opals from other sources.But what exactly IS an Opal?
Opals are a gorgeous natural gemstone beloved for their play-of-color and iridescence and are made of hydrous silicon dioxide. Opals are a fascinating stone in that they technically don’t have a definitive chemical composition. The chemical makeup of opal changes from stone to stone because the amount of water in each stone varies. The internal structure of opals is regularly packed microscopic silica spheres that reflect and refract light like a prism to give off that play-of-color. No two opals are ever the same even if they're from the same mine or deposit.
The way an Opal is formed matters greatly to the stability and durability of the stone.
Australian opals are mined deep beneath the surface of the Earth. Australian opals grow against sandstone or ironstone host rocks deep underground in geothermal water that is millions of years old. Because they are formed in water, Australian opals naturally contain a high volume of water and are non-porous, meaning they don't absorb any additional liquids. Most Australian opals used for jewelry contain about 5-6% water.
Ethiopian opals grow in large volcanic deposits high up in the Ethiopian hills formed in between layers of igneous rocks. Silica bearing waters once accumulated on top of the impenetrable clay underneath the layers of volcanic rock. As the water evaporated, the silica gel then precipitated into the spaces between these rocks and formed opals. Most Ethiopian opals are hydrophane, meaning they are porous, so they can absorb water or other liquids which can change their base colors, transparency, play-of-color, and size.
Hydrophane opals have durability issues. Aside from changes to color, size and transparency; cracking or crazing (spiderweb like fractures along the surface of the stone) can occur when the stone absorbs water. It takes several hours of immersion for an opal to absorb enough liquid to create these changes and a hydrophane opal can lose the water it gained if allowed to dry. This can take several weeks, and the opal should return to its natural state visibly, but it can greatly affect their durability and stability and any cracking or crazing will remain. Some hydrophane opals can absorb enough water to increase their weight by 15%.
Because of it’s beauty, uniqueness and stunning play-of-color, the best opals can command prices per carat to rival diamonds, rubies, sapphires and emeralds. Australian opals have a reputation for being some the most expensive opals on the market and there are several reasons why.
While opals are mined in several places throughout the world, Australia has commanded the market for over 100 years, with 95% of the worlds precious opals coming from the continent. Ethiopian opal is actually a relatively newer find from the ‘90’s. When it comes to gemstones, in most cases the rarer the stone the more expensive, but despite the abundance of Australian opals they garner such high prices not just because of their notoriety and prestige but also because of their much higher quality. Because of the natural water inside Australian opals, they are also denser than hydrophane opals, creating higher carat weights for smaller sizes.
CARING FOR OUR OPAL
Opals in general are fragile stones, a 5.5-6 on the Mohs hardness scale. They are soft and easily chipped. Australian opals have tighter bonds of more densely packed silica spheres and are stronger than Ethiopian opals but can crack with hard impacts. You can wash your hands, use hand sanitizer, swim, and bathe with our Australian opal jewelry but it’s best to take them off before working out, using household cleaners or doing any hard labor. Because of their porous nature, hydrophane opals should avoid any humidity changes and heat in general. Australian opals are fine with heat and humidity fluctuations but should avoid them in extreme cases.
Never use an ultrasonic cleaner for any opal, vibrations can cause cracking and crazing. To keep your Opal jewelry bright and shiny, clean opals with mild liquid soap and a soft cloth or brush. Because opals are soft, over a long period of time they may lose their luster due to small abrasions to the surface of the stone, in this case the stone can be re-polished by an experienced jeweler to its original shine.