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Opal Information

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. Lucky for you at Opal Auctions we have all the different types of opals so you can easily explore and understand the difference between them. In this article we are going to explain each of the different types of opals including Black Opal, Crystal Opal, Boulder Opal, Yowah and Koroit Opal and the smaller Opal fields like Mintabie and Tintenbar. Also we will talk about the important international Opals from Ethiopia, Mexico, Honduras, African and South American Opals. AUSTRALIAN OPALS

Andamooka Opal

It is only a very small Opal field but is known 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 is by far the most popular and well know type of Opal. It is characterized as Opal that has a dark body color. To understand how to judge the body tone of an Opal be sure to check this article.

Take note that the term Black Opal does not mean that the Opal is dark or dull. Some of the brightest and most beautiful opals are Black Opals. The term simply refers to the body tone of the stone.

Most black Opal is mined in Lightning Ridge, NSW, Australia. When people talk about Black Opals they are referring to stones that have come from this region.

Dark Opal

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

Using the Base Body Tone chart you can see that a 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. While this Opal is beautiful it does not show off the Opal colors as well as the Black Opal.

This is because Black Opal amplifies the colors with the contrasting dark background. Most White Opal have muted pastel colors.

Boulder Opal

Boulder Opal is Opal that has formed along with another rock called ironstone. Most of this type of Opal comes from the Opal fields in Queensland where there is a huge belt that spreads thousands of kilometers where this type of Opal is produced.

The main thing to notice with Boulder Opal is the striking red ironstone that is present within the Opal.

Within the realm of Boulder Opal there are various types which deserve their own mention-

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 such a beautiful 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.

Matrix

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

Boulder Opal is natural but Boulder Fairy Opal is cooked sandstone Opal and therefore treated.

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 an inland sea millions years ago, so today you can find, if you’re lucky, opalised marine life including sea shells, belemites and opalized marine life to remains of huge dinosaurs. It is rare to find pieces that are opalised but many collectors enjoy these unique specimens.