Opal, one of the two birthstones for October, is an amorphous form of silica which has become the national stone of Australia.
The stone’s internal structure causes it to diffract light, giving it the ‘rainbow’ colors for which it is most famous.
Precious opal is known for its exciting interplay of colors, displaying almost all the shades of nature. Stones are found in any color from clear through to white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. It also varies from opaque to semitransparent depending on the conditions in which it formed.
Opal measures between 5.5 and 6 on the Moh’s scale, making it a rather vulnerable stone that can easily be subject to knocks and scratches through everyday wear. However, because opal becomes paler in dry conditions, some experts advise wearing opal jewelry frequently in order to give it the humidity required to retain its beauty.
As much as 97 per cent of the world’s opal is found in Australia, but Ethiopia is another large producer of the stone.
Opal plays a key role in aboriginal Australian culture, and legend has it that its creator came down to Earth on a rainbow, bringing the message of peace to all the humans. Where his foot touched the ground, the stones began sparkling in all the colors of the rainbow – and this was how opal was born.
Roman scribes wrote of opal as a stone that possessed the perfect combination of characteristics. And in the Middle Ages, its array of colors earned it the reputation of having the power of all gemstones in one – Shakespeare, for example, referred to it as ‘that miracle and queen of gems’ in his famous play Twelfth Night.
However, i[ until large blocks of opal were first found on an Australian cattle station in 1849, the stone had been incredibly rare. And only in the 1960s were opal’s incredible colors finally explained by scientists. It’s now understood that small spheres from silica gel cause colorful interference within the stone.
The main characteristics affecting the value of opal are its base color, body tone, ‘play of color’ and brilliance.
Black opal is by far the most prized opal and can fetch prices of more than $10,000 per carat. Generally speaking, if the stone has a vibrant play of colors and the range of those colors is wide, it will rise in value – but because opal’s colors and patterns vary so much from stone to stone, it is sometimes argued that there is no set system for measuring its value.
Sugar-acid treatment is the most common way that opals are enhanced.
The process, which involves drenching it in a sugar solution and boiling in sulphuric acid, is believed to improve opal’s play of colors.
Opal is a fascinating stone, both for its playful array of colors and the fact that it seems to need to be worn in order to keep its beauty.
Used in a protective setting, opal is a beautiful and enchanting choice for eye-catching jewelry.