Opal Information

Australian Opal Specialists

Constable and Co are Australian Opal Specialist. There are so many types of Opals on the market that it can sometimes be overwhelming to try and identify them all. At Constable and Co we have all the different types of Australian Opal. Below is a brief description of each of the different types of opals including Black Opal, Crystal Opal, Boulder Opal, Yowah and Koroit Opal and the smaller Opal fields like Andamooka, Mintabie and Tintenbar.


Andamooka Opal :

It is only a very small Opal field but is known for its gem crystal Opal and in recent times for its treated matrix Opal sandstone and has spectacular colours.

Australian Fire Opal :

This Opal field is only new and situated in the deserts of Western Australia and the Opal has resemblance to Mexican fire Opal. It comes in brilliant sun burnt orange to red color.

Black Opal :

Most black Opal is mined in Lightning Ridge, NSW, Australia. The name Black Opals refers to stones that have come predominantly from this region and the term simply refers to the darker body tone of the stone

Dark Opal

Dark Opal is Opal that has a dark base but that is not dark enough to be called Black Opal.

Using a Base Body Tone chart Black Opal has a body tone of N1 to N4. Dark Opal however has a body tone of N5 to N7.

White/ Precious /Fire Opal:

White Opal refers to Opal with a white milky body tone. Most of this type of Opal comes from Coober Pedy in South Australia and White Cliffs in New South Wales which is also famous for the Opal Pineapple formations.

Boulder Opal:

Boulder Opal refers to the natural ironstone base of the Opal. The Opal form in thin cracks and fissures in the sedimentary ironstone and when cut to a precious gem stone part of the natural host ironstone is left attached the precious Opal, like a painting on a canvas

Koroit Opal:

This Opal is so unique because it has such an amazing appearance. The cracks in the ironstone are filled with precious Opal giving it a patterned look. This Opal is very similar to Matrix Opal however, Koroit Opal has pure ironstone as the main stone.

Yowah Nuts:

These are only found in Yowah, Queensland. They are nodules of Opal that when cracked open can contain a pocket of solid precious Opal. Most of the nuts that are mined do not contain anything but every now and then a spectacular Yowah Nut is unearthed.


This type of Opal can be a matrix of ironstone and other stones together with precious Opal. It can also be a matrix of sandstone, clay and ironstone.

Solid matrix opals from Andamooka are much more expensive than concrete matrix in rough.

The term “sugar treatment” refers to carbonization. Also, because there are other methods to change base color of matrix opals than just boiling in sugar and acid and the result is the same: filling pores with carbon.

Fairy Opal:

Found predominantly in the northern Boulder Opal fields it is a natural Sandstone matrix commonly called Fairy Opal is cooked/treated similar to the Andamooka Matrix to show its vibrant colours

Mintabie Opal:

Famous for creating milky white and sometimes Black Opal. It is located in South Australia and has produced some of the largest, most beautiful Opals in the past.

Tintenbar Opal:

A very small volcanic Opal field in NSW, the Opals are not very stable and are deep dark hues and make excellent doublets.

Opal Fossils:

Australia once had a great inland sea millions years ago and the receding water left the fossils of a great variety of sea life of the day. These are found mostly in the southern Opal fields and are mostly opalised marine life including sea shells, belemites and opalized marine life and though to the fossils of dinosaurs. It is rare to find pieces that are opalised but many collectors enjoy these unique specimens.