The finest and most valuable of all Opals was first discovered in Lightning Ridge in New South Walls, Australia, in 1877. Black Opal is much more precious than white opal, not even close in its value or price.
Only Mined In Australia
Unlike White Opal and Fire Opal, Black Opal is only mined in Australia. Besides the famous mine of Lightning Ridge, "Mintabie" mine is known for producing gray or blackish gray body color opals
Black Opals Are Not Always Black
"Black Opal" is often used as a generic term to describe any Opal, which has play of color against a dark body color. If the body color is mid-gray to gray, some Opal dealers will describe it as a semi-black Opal. The definition has been always relative and the borderlines between black and semi-black or gray Opal may vary between dealers.
How To Evaluate Black Opal
1. Base color: also called body color, the darker the body color is the more valuable the Opal.
2. Color pattern: also known as "play of color" the most valuable color pattern is red and orange, blue, purple and green come next. The stronger the play of color is, the more valuable the Opal. This is sometimes referred to as "Fire." If you see this Fire from all angles, you have a little treasure.
3. Hue: like any other color gem, the better the hue the more valuable the Opal.
4. Color pattern division: the bigger the color parts are, the more valuable the Opal. Those Opals that exhibit small dots of color is called "Pin-Fire," are less valuable, even though they may exhibit excellent fire. Blue Opal with blackish body color is also valuable. The more the blue or the purple play of color, the more valuable the Opal.
Black Opal Is More Stable
Because Opal is silica that naturally contains water, some of it tens to dry out and crack, which can happen anytime if sudden change of temperature occurs. For that reason dealers usually keep rough Opals in jars of water. It is known that Black Opal has a lower percentage of water content compared to a White Opal, which makes it more stable.
This is a confusing subject that most Opal buyers don't understand the difference between a beautiful Opal with natural color pattern division and a cracked one. Similar to the subject of fractures Emerald or included Emerald.
Color Pattern Divisions, Crazing, and Fractures
1. Color pattern divisions are irregular lines between color that divides and separates them and looks like fractures but it is not and never affects the Opal durability and hardly develops fractures.
2. Crazing are internal Opal inclusions that do not reach the surface unless they are developed into fractures, they do not affect the Opal durability. Crazing is always caused by drying and can be prevented by keeping the Opal in water once in a while or by impregnating it with oil.
3. Fractures are external cracks that affects the durability of the Opal and destroys the value, Opal fractures can't be repaired, however they can be avoided by avoiding sudden change of temperature or excessive heat.
Boulder Opal
Boulder Opals are usually veins of beautiful Opal grown in spaces within the boulder host rock, which is usually Ironstone. The quality and value of the Boulder Opal depends on the amount of the play of color and the Opal veins, some of the Boulder Opal matrix when polished naturally grows with beautiful artistic screen. Boulder Opal is less costly than Black Opal because it is usually not a solid Opal; it is layers of Opal naturally grown within a matrix.
Yowah Opal
Another type of matrix Opal that is completely natural mined in Yowah, South Queensland. The patches and Opal veins grow its ironstone matrix are usually of very distinctive and unique patterns. Most of Boulder and Yowah Opals are polished in irregular shapes called Free Forms to preserve the beauty of the Opal spots that are randomly "naturally" scattered throughout the matrix.
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