When we talk about types of opal we are referring to the major classifications we use in the opal shop.
Australian black opals are the rarest type of opal ever found and can fetch the highest price per carat than any other opal in the world. What makes a black opal so rare is the phenomenon of dark to black underlying body tone or potch, which helps to intensify the brightness of the color bar. On the body tone scale, black opal will sit between N1 to N4.
The body tone is guaged by the face or top of the gem and should not be confused with play of color. The body tone of an opal should never be determined by the back of the gem. However, the potch in a black opal usually found on the back of the gem can help the overall body tone to become darker, as long as the potch sits directly behind the color bar naturally helping the play of color to become darker.
Black Potch is the main reason why black opal is so rare. Potch, also known as common opal, which is opal silica, has no real value unless there is play of color. Most opal fields produce common potch but black potch is predominantly found in Lightning Ridge with gem play of color. Some other areas that have produced black opal are Mintabie and Andamooka.
Side Note: A black opal can also have no potch on it at all and instead has a very dark tint to it, almost like tinted glass, where you can still see through it when held up to the light. This is called a black crystal opal and is considered very rare and valuable.
Crystal opals can come from every opal field in Australia and is the closest rival in value and quality to black opal. They are a semi-transparent type of opal, meaning when held up to a light source, distorted images and light can be seen through the gemstone.
Crystal opals have the most depth when it comes to color on color or play of color because of their glassy transparency. Having no or very little potch, crystal opal is usually all play of color, giving it the ultimate 3D color-on-color effect. When a crystal opal is completely clean of inclusions you can polish the back of the gem to get the full potential of play of color.
Side Note: Secretly crystal opal is Justin’s favorite type of opal and his private collection is made up of more crystal opals than any other type.
Dark opals have a body tone lighter than black opals and darker than white opals and sit on the body tone scale of N5 to N6. It is opaque like a black opal but it has a slightly lighter body shade. Dark opals can be found in every opal mining area in Australia and would be considered one of the most common types but not the least expensive.
The play of color, brightness and pattern of a dark opal is what gives it its value, yet the body tone of a dark opal is what makes them worth less than a black opal.
Side note: It is a great choice if your budget is not as high as black opal.
Boulder opal is a unique type of opal that is only found in Queensland and is one of the most sought after types of Australian opals.
Boulder opal has an attribute like no other due to its formation in an ironstone host rock, found in brown ironstone boulders. The opal is usually formed in thin veins through the ironstone and has to be opened or split to find the face of color. The face of the boulder opal is mostly undulating because it follows the natural seam in the boulder. Often we refer to a pair of opals with the same pattern as a boulder split because it has been split down the middle of the vein of color creating two faces with the same pattern and color.
Side note: It is common for boulder opal to be cut into freeform shapes and picture stones rather than perfect oval and symmetrical shapes.
Most white opal comes from Coober Pedy but can be found in every opal field in Australia and also the world. This type of opal was one of the first discovered and taken to market and it’s what most people visualize when discussing opal.
White opal is a translucent milky type of opal that has a body tone of N7 to N9. While it can have a very bright play of color, the milky white background or body tone can partially detract from the brightness and play of color.
Unlike crystal opal which is transparent and allows you to see distorted images through it, the white opal will only allow light through with no transparency. It’s a fine line where white opal becomes a crystal opal.
Side note: Coober Pedy is the town where most people live underground, unlike Lightning Ridge, where everyone lives above ground.
Opal Patterns are up next
Every opal is unique and the arrangement of silica spheres create amazing patterns. Discover the most recognized ones in Lightning Ridge opal.