Below is the entire list of Johno's blog posts relating to Opal Types.
12 March 2024 by Johno
Yowah nutsWhat is a Yowah NutA yowah nut is a form of Boulder opal. It is found in the shape of a nut and these nuts can vary in size up to the size of an avacado. They are usually hollow inside a shell of a form of ironstone and these hollows...
11 March 2024 by Johno
Polishing shellsIf you have ever picked up sea shells you will have noticed that many of them have a pearl like appearance beneath their outer coating. When this coating is removed the appearance of the shell is greatly enhanced.I have been tempted on many occasions to grind this outer coating...
7 April 2023 by Johno
Grey Potch.I had recently purchased a parcel of opal that contained quite a lot of potch as well as some nice colour. I put the potch to one side and forgot about it. Last week I went through it again and saw what I thought was a faint red band...
22 June 2020 by Johno
Trying something different with your opal Most opal lends itself to cutting some form of cabechon. Some will have rounded tops and others, where the opal has a band of colour, will have flattened tops to ensure we get the most out of our opal. When we have thin layers of opal...
2 December 2019 by Johno
Andamooka Matrix Opal Andamooka Matrix opal is a unique form of opal found only at the Andamooka Opal field in South Australia. It consists of a fine grained limestone rock with opal ingrained in this limestone matrix. The opal can exist in all sorts of patterns. Because of the...
21 November 2019 by Johno
A little while ago "Mac" contacted me with his theory on opal formation. I have my theory on this topic but it is good to keep an open mind as none of us were around when opal was formed. Mac has given me permission to present his thoughts on...
20 October 2019 by Johno
A friend in Ballina, who's father owned a mine at Andamooka many years ago, has reached the stage in his life where he wants to sell off his collection of opal. I have agreed to put some of them on this website to see if anyone out there is interested....
21 January 2019 by Johno
How was Australian Precious Opal Formed. I have read many many different articles on how Australian precious opal was formed but have had some doubts on the commonly accepted theory of water seeping through sandstone and dissolving silica ,which then formed a gel and seeped into cracks and crevices...
24 May 2017 by Johno
Andamooka Matrix Opal Recently Ross from NSW contacted me and asked if I could treat some Andamooka Matrix Opal his father had found some time ago, when he mined at Andamooka. Ross apparently has quite a collection of Andamooka Matrix opal and is looking to sell it. If anyone...
24 December 2016 by Johno
Crystal Opal Crystal opal is so named because you can see right through it when you hold it up against a bright light. You can't see any of the colour play when you do this but let the light reflect off a good crystal opal and you will see...
23 October 2016 by Johno
Boulder Opal Boulder opal is a special form of opal found only in Queensland. "Boulder opal" is the result of opal forming silica penetrating cracks and crevices in ironstone boulders. Formed millions of years ago, amorphous silica seeped into random cracks or in between concentric layers of ironstone...
6 March 2016 by Johno
Australian Opal Ausralian Opal is arguably the most beautiful and stable opal in the world. It is an amorphous form of Silica with a water content varying from 3 percent to 21 percent but usually within the range of 5-10 percent. Amorphous is defined as "without any clearly defined...
2 January 2016 by Johno
Lightning Ridge Opal Field Lightning Ridge Fossils are among some of the most amazing fossils found any where in the world. At Lightning Ridge opal is usually found near the interface of the Wallangulla sandstone and the Finch clay facies (called the opal dirt). The opal is found...
17 November 2015 by Johno
I am sorry to have to delete the content of this post. Andre has instructed me to remove all of his photographs. Johno...
10 November 2015 by Johno
The Desert Sea Collection The Comfort Inn Experience Motel at Coober Pedy is famous for it's owners great collection of opalised sea shells known as" The Desert Sea Collection". In March 2014, Andre was in Coober Pedy and was shown this collection. He also photographed the Desert Sea...
5 November 2015 by Johno
Andamooka Matrix Opal Andamooka matrix opal is still a much maligned form of opal in many people's minds. The fact that it is a treated form of opal seems to ignore the fact that it is still basically one of natures treasures with it's beauty enhanced by changing the...
1 November 2015 by Johno
Opalised Fossils Opalised fossils are one of natures greatest treasures. Opal can hide many surprises. Because opal was generally formed at the bottom of the sea or swamp, it has replaced many interesting things. Sea shells, fresh water shells, sea creatures, bones and plants have all been found transformed...
5 May 2015 by Johno
Andamooka Rainbow Matrix Opal is fast becoming popular with those who can't afford a "Real Opal". Originally it was called "concrete" because that was what it looked like although you could see small specks of opal in amongst the concrete like grains. It is a porous quartzite host rock...
6 October 2014 by Johno
More Andamooka Matrix Opal During the last month I was contacted by Andre who told me he had a couple of pieces of Andamooka matrix opal he had collected some time ago. He purchased one of these from Cash Converters and they were part of a deceased estate. Andre...
4 August 2014 by Johno
Opal is a form of silica which has water molecules attached to it (varying from 3% to 21%) and is called hydrated silica. It is an amorphous material, which means that it does not have a crystalline structure. It's internal molecular structure can be ordered. Opal consists at a micro...
27 May 2013 by Johno
Whenever we think of opal we usually think of gems used in jewellery, but there are some opals and other gemstones which portray beautiful and intriguing patterns, but which are not necessarily suitable for use as jewellery. Some of the stones shown below are from my collection and while...
30 April 2013 by Johno
Opal at Andamooka is found in a narrow band of depths varying up to 600 mm. In this bed there are many boulders of strongly bonded quartzite of varying sizes.,Today, as you wander among the great piles of disturbed overburden which is mixed with the old opal level , you...
30 April 2013 by Johno
The opal fields of Australia were formed at the bottom of a large inland sea. In this sea there were all sorts of marine creatures including turtles, crocodiles, dinosaurs, all sorts of fish and of course shellfish. As these creatures died their bodies sank to the bottom of the sea...
14 February 2013 by Johno
Yowah is a small outback opal town in Queensland located about 1,000 km west of Brisbane and about 130 km west of Cunnamulla.There is a sealed road all the way so it is very easily accessible. The opal field surrounding Yowah is quite small, being about 4 square kilometres. It...
13 February 2013 by Johno
If you have any thin pieces of opal with nice colour but believe it is too thin to cut a cabechon then think about making a doublet. A doublet is basically a fairly thin layer of usually opal glued to a thicker layer of opal potch or some other...
23 January 2013 by Johno
For all of us amateur opal cutters getting a regular supply of reasonable quality is one of the major problems. As opal mining slows down due to rising costs and lack of new finds, it is getting harder and harder to access. I have been lucky living in Australia...
17 January 2013 by Johno
The term matrix opal refers to a type of opal where there is a base stone with tiny pieces of brilliant opal interspersed within this base stone. The base can be limestone, sandstone or even ironstone. At Andamooka and apparently nowhere else in the world, two types of matrix opal...
15 November 2010 by Johno
Andamooka matrix opal is basically a limestone base rock impregnated with tiny pieces of precious opal. Because the limestone is very pale it is often difficult to see the play of opal colour in the stone and hence a method of darkening the limestone background was developed so the colour...