The white opal remains less valuable than the black opal or the boulder opal precisely because of its less brilliant play of colours and relative abundance. The white opal is often also referred to in some circles as the 'milky opal'. Here are some of its characteristics:

Appearance

What makes the white opal distinguishable from its other opal counterparts is its pale white or light body tone. There is a body tone chart that professionals use when determining whether an opal is a white opal or not. As in the case with other opal stones, the white opal may also displays a fantastic 'play of colour'.

More often than not, a white opal will also have pale white potch (colorless and valueless opal) remnants on its back. In other cases, this potch may be present all over the stone, affecting its 'play of color'.

As you can imagine, the white opal does not have the same vibrancy as its black or boulder counterparts. Although the stone might be pure, its white colour makes it difficult for a person to see and distinguish different colours within the spectrum. The dark body tone of black opals and boulder opals make this much easier.

Value

In comparison to other opals like the black or the boulder types, the white opal comes in last. It is far less valuable than other kinds of opals because of its relatively poor vibrancy. Another important factor that plays a part in determining the value of an opal is its abundance. The white opal is commonly mined, and therefore readily available for purchase.

While it is the case that most white opal stones' pale colour makes them less sought after, it is also possible to find a white opal of superior quality that is extremely beautiful. Such white opals have been purchased at prices rising up to AUD $200 per carat. Other factors that affect the value of the white opal are its brightness and colour patterns.

A Word on Crystal Opals

Crystal opals are often confused with white opals. There is a fine line of difference between the two, but crystal opals are generally identified as those stones which have transparent or translucent properties. When there is only a mild translucence, it becomes difficult to determine whether a stone is a crystal opal or a white opal.

Origin

Coober Pedy, Andamooka and Mintabie are three of the most common places where white opals are mined in Southern Australia.