If you were born in October, then you have one of the most unique and exciting gemstones of them all, opal. One of the great things about opal is that it comes in so many different varieties that you can collect dozens of opal jewelry pieces and they will all be different. We explored the virtues of opal in a previous article, but we thought we’d discuss some of the lesser known facts about this gorgeous stone in this article. Here are five things to know about opal.
Black opals are the rarest
Opal comes in every color of the rainbow, and in many varieties of opal, you can find every color represented within a single stone. However, aside from the play-of-color, which we’ll explain later, there is the background color. The majority of opal jewelry has either a white or green background, but black opals are the rarest, and usually the most coveted. This is because the black background makes the sparkling crystals within the stone really pop like stars in a dark night sky.
It is the national gemstone of Australia
The majority of opals are found in Australia, which is why it is the national gemstone of Australia. In fact, at one point in the Earth’s history, there was a shallow sea in what is now known as Lightning Ridge, and this is where many of the world’s opal jewelry is mined. Opals are a form of hydrated amorphous silica, and they form in the fissures of just about all rock varieties. They are composed of about 6-10% water and deposited at very low temperatures.
Fossils can become opalized
During the early Cretaceous period, back when dinosaurs were roaming the planet, massive marine reptiles inhabited this shallow sea over much of inland Australia. When these reptiles died, their bones were deposited into the seabed and began to decompose. During this decomposition process, opal deposits filled the void in the rock where the bones used to be, forming exact replicas of those fossils. Australia is the only place in the world where opalized fossils are found and they provide proof of some of the most peculiar marine reptiles that have long since been extinct.
Opals are sensitive to heat, light and dryness
Because opals are made of hydrated silica, they can very easily dry out and lose their clarity. Drying out leads to cracks and fractures, often spreading throughout the stone like a spider web. This can severely reduce the value of the stone. That’s why opal jewelry should never be displayed in windows or exposed for long periods of time to direct sunlight.
Play-of-color is a very important factor
Aside from the background color, the play-of-color is a major factor when determining the value of an opal. The more colors that are represented and the more angles from which those colors can be seen, the more valuable the opal.