Anyone treated fairy opal before?

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I was visiting a friend yesterday, when he showed me a cooking pot with some brown liquid in it. On closer inspection i saw it had rocks in it.
When we started pulling out the rocks some beautiful color appeared. He explained to me that it was fairy opal and he was treating it with sugar to bring the color out.
He went on to say that it couldn't be cabbed because the rock was a sandstone and was too porous so he was experimenting by pre shaping and then cooking.

I was lucky enough to be given a piece to play with and started doing a little reading. From what i have seen it seems that fairy opal can be treated with either oil or sugar, but then it needs to be stabilized after.
The only hint to stabilization was when liquid glass was mentioned, but another company seem to have a method of stabilizing so they can grind and polish rather than relying on the epoxy as a finish.

Just wondering if anyone has had any experience in treating fairy opal and if there are any tips?



 
My old man had just been up there not long ago and explained the odd sugar soak n bake methods 8)
rather trippy stuff i say! From what I remember, it seems the rocks cant be polished by cab and Im pretty sure he said he just used clear nail polish 2 coats for final look? You got a rippa sample!
 
Cheers AR, i started getting a bit worried as i read a few methods that involved soaking the stone in concentrated sulfuric acid after the sugar treatment. But i believe this is for the andamooka matrix opal, which i believe has a limestone matrix rather than sandstone.

I have some opticon that i brought to treat porous bolder opal and may give that a go after i treat it. Not in a hurry so i will keep reading at the moment.
 
Hi shivan.
Whilst I have never had anything to do with this type of opal during my last cutting course the instructor touched on this method.
My understanding is the sugar /acid treatment is instead of polishing as it leaves the matrix with a clear gloss finish.
The liquid glass is a two pack that is applied to a stone to fill in any imperfections and as before it cannot be polished after application.
But the results are supposed to be quite good.
 
It is pretty but given the size and the relative lack of colour per sample size I wouldn't expend too much effort if any if you were looking to sell it, there is heaps of opal on dark matrix around which give a far better result. But as a specimen one solution I heard of is to soak the specimen in multiple dips of very diluted mix of water and aquadhere which then sticks loose material together but also seals and coats the rock which might be a useful trick if you slice and flatten on a wheel first. This technique is used to stick and coat fragile crystal specimens together as told by a seller of crystals but I have never tried it.

Jon
 
Cheers for the info blisters. Have not heard of the aquadhere before it looks interesting. May be a cheaper alternative to opticon.

The piece i have seems to show color around the middle more than the top or bottom. I will just be happy if i end up with a small specimen piece but will probably take a slice and maybe have a play with shaping before i treat it.

I am not under any illusions with the bit i have, when seeing rocks that were already treated i noticed some showed color a lot better than others and i have no idea what they looked like before being treated.
Its more out of interest that i would like to have a play. Plus if i could figure out a decent way to stabilize it would help the gent that gave me the piece as i believe he is just using liquid glass at the moment.
 
Gday Mate,

The only fairy treatment I have seen is with the Adamooka matrix opal - they used sugar and a whole lot of acid to get the colour out with good results.
The acid was key, the miner was going on about how its now a controlled substance and you cant get loads of it anymore.

In terms of boulder i havent seen results of a similar caliber/success as its a completely different stone.

Sorry I couldn't be any more help.

Jukey
 
Cheers Jukebox, its defiantly not andamooka (which from my understanding is a limestone matrix?) from what the bloke told me.
The opal in the rock seems to be in grains rather than seams or veins like the bolder opal i have seen, though you would know a lot more about opal than me.

As it was a gift to experiment with, there is no loss if i mess up. I will probably end up cooking it with sugar and treating it with opticon to stabilize. Even if i don't get the color he did on his pieces, if i can work out a decent way to stabilize for polishing it will be worth it.
 
A lot of fairy opal i have didnt need to be treated once polished up - let me know how the treatment goes i have buckets of the stuff!
 
I used to mine opal in Coober Pedy in seventies and had friend in Andamooka. He used to make pretty cabs from matrix opal, using sugar and sulphuric acid. What he explained to me is that the sugar fill pores in the stone and the acid converts sugar to carbon. He told me it should work on any porous stone.
Karl
 
Yes, I have seen it mostly done at Andamooka. They get a small price for this as decorative stone. Not in limestone there. As KarlS says it gives a dark matrix by converting sugar to carbon.
 
Goldierocks, i have personally never been to any opal fields yet (still hope to do the rounds one day) and am sure not all opal in Andamooka is in limestone, i believe the majority is in shale, but from my understanding the Andamooka opal matrix is in limestone, just wondering why you say its not? I keep hearing and reading so much contradictory information it can get frustrating sometimes.

Again the piece i am playing with is not Andamooka, i believe it is from somewhere closer to Mintabie. In the process of setting up the garage, so wont get a chance to have a play for a while yet.

From https://www.facebook.com/notes/aussie-opal-diggers/treating-andamooka-matrix-opal/356305997845221/ :
"Opal at Andamooka exists in the thin marine Bulldog Shale, which is the significant portion of the Marree Subgroup of Early Cretaceous period.

It is usually overlies Algebuckina Sandstone or tours directly onto pre-Mesozoic stones. The top sub-unit of Bulldog Shale referred as kopi by the miners, which compromises with high- weathered and white-sandy clay with dotted, huge changeable boulders. At the bottom of the kopi, there is a wide-ranging and sandy boulder bed.
It is referred as a solid or multinational band, which consist several stones, cobbles, and stone of pre-Mesozoic rocks, primarily Arcoona Quartzite. Underneath the conglomerate band is a fair brown, yellow or grey clay stone with a low-sand substance known as the mud. Opal at Andamooka takes place primarily at one perspective, referred by the miners as the level.
With the contact of the multi-national band and the muck, other sub-levels (squibby levels) that transpire above the major level, but none are as well-known, permanent or dynamic. The main opal diversity generated is crystal opal (visible to transparent). Matrix opal is grey stone with sparks of colour, which is usually formed as an alternative of limestone boulders.
In fact, both matrix opals can be treated by drenched and through the use of sugar solution and boiled sulphuric acid to cast a shadow the body tone as well as, to improve the play of colour. The tough rock, termed stone by the miners, which is 50 metres in thickness, the base, which resembling the bottom of the Stuart Range escarpment.
Through this weathered zone, the rock is usually bleached in white or multi-coloured, silty or dirty clay stone with kaolinite as the leading clay stone. The setting of the weathered contour varies, and most of the opal miners think even slight variations, which is significant in finding opal."

http://lapidaryworld.com/pdf/Treating_Opal.pdf
http://www.johnosopals.com/2010/11/treating-andamooka-matrix-opal
 
I am a geo doing a study of all the opal fields and have visited them all on a 7 week field trip (and before and since). Not aware of any in limestone opal host at Andamooka, certainly all "fairy stone" that I have seen is sandstone (there are multiple elevations of opal though). You say "Matrix opal is grey stone with sparks of colour, which is usually formed as an alternative of limestone boulders". That does not make sense to me (grammatically or geologically) - I suspect a typo or something. There are some carbonate rocks in the Cadna-Owie Formation and some minor carbonate grains as sparse matrix in some other sandstone so it is not impossible - maybe they are saying that the opal in fairy stone fills tiny cavities left when the few carbonate grains of a sandstone matrix weather out (definitely possible). If so, the proportion of carbonate grains ("limestone") is and was tiny, because the proprtion of opal in the rock is small as specks and any carbonate left would dissolve during acid treatment and spoil the fairy rock. A geologist would not call the rock limestone either way.....

However I was referring to your comment that "definitely not andamooka (which from my understanding is a limestone matrix". I have seen fairy stone from various fields but mostly from Andamooka, and most opal at Andamooka is not in limestone. Fairy stone is not my interest - a low value, modified rock ised to make a few bob from stuff otherwise worthless, Looks nice in aquariums etc.
 
Again please do not think i am saying you are wrong goldierocks, i am just trying to get my information straight.
I only started reading a bit about the Andamooka matrix opal because there was a lot of information on treating it, as oppose to fairy opal (sandstone matrix which i was asking about to start with).

This interested me as i had not heard of opal forming in limestone. Unfortunately as i have two kids and a homeloan and am studying with little work, all i can do is read about these places and hope to be able to visit one day ( Don't suppose you are looking for an unqualified assistant at all? ;) ).

The link i posted was probably not the best, but that and the other two links i posted below all refer to the Andamooka matrix being limestone. Though these are more lapidary links than geological, but as there were so many references to it being limestone i assumed they knew what they were talking about. Will keep reading and see what else i can come up with.

From http://lapidaryworld.com/pdf/Treating_Opal.pdf
"Andamooka matrix opal:
Strictly from the sense of its physical formation, all opal is formed in
cavities of opportunity. Sometimes the cavities are large as in 'slides' or
'levels' which produce thick solid slabs; sometimes isolated as in a clam
shell; and sometimes intruding into fine fissures in hard native stone such as
ironstone.
But when opal filters into ancient layers of limestone, something truly
miraculous occurs.
Limestone is formed over millions of years by the death of countless
microscopic plants and animals in waters and bays. The Cliffs of Dover are
a well known example. The skeletons or fossils of these early life forms
persist, and create myriads opportunities for the intrusion of opal, if the
conditions are right.
The microscopic cavities in limestone prevent the opal from forming what
we recognize as solid opal with thick layers of fire. However, the opal does
form the microscopic equivalent, within these tiny cavities. With the aid of a
microscope, one can see a reticulated effect, varying somewhat between the
eye of a dragonfly and the skin of a snake.
Limestone appears to us usually as a very white chalk-like stone. This is
detrimental to the fire of any opal which has intruded the matrix. There is
too much diffraction of the light for any specific color to assert itself to our
eyes. Therefore, in the natural state, limestone containing opal appears to
have color, but it is washed out and faint. For this reason, it was not viewed
as marketable when first discovered.
But when the matrix is wetted, that unmistakable opal fire is there, and no
doubt much time went into thinking about just how this material might be
treated.
One place in the world where limestone matrix opal occurs, is in a small
area of South Australia called Andamooka
"

And from http://www.johnosopals.com/2010/11/treating-andamooka-matrix-opal
"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 of the opal could be seen."
 
Cheers Mr Magoo, that was another of the links i have found in my searches.

I had also wondered about the treatment of acid on a limestone, but had just put it down to the sugar treatment somehow stabilising the limestone before the acid...

Again i was only going off what i had been able to find so far, but i find the lapidary world a funny place. It seems full of myth, word of mouth and made up names for common minerals and rocks in a bid to sell them for more money.
 
Shivan - the fuller description makes more sense. I don't remember seeing it, but it may well be present in small quantities and I have no reason to doubt it given the description (I was also confusing fairy opal and matrix opal - they are not strict geological terms and therefore I don't use them). More a case of whether it just occurs at Andamooka (as it may) or dominates (which I don't think it does). I would not expect the sugar to do anything to stabilise it. The sugar solution enters the pores of the rock - the acid then reduces the sugar, a carbon-bearing compound (C12H22O11), to carbon and thus gives a dark colour to the matrix. The purpose of the sugar is as a compund to convert to carbon to give the black colour. I remember as a kid we used to mix potassium nitrate and sugar then add acid (don't do it - the reaction generates heat and will explode, we let the acid soak through cotton wool to get away)- giving potassium nitrate plus carbon (gunpowder). Stupid kids. Much like ANFO we use in mines - a mixture of ammonium nitrate and fuel oil, which is nice and stable to pour down drill-holes until you add a stick of gelignite with detanator to it when you blast. Even then it can be unstable (a cement mixer mixing the stuff wiped out the port of Halifax, Nova Scotia, years ago).
 
Shivan, I chased down the answer. I could not recall seeing limestone beds in the mines at Andamooka, but I now know the answer. There is a conglomerate bed in part of the rock sequence which contains boulders of various rocks, and some are limestone boulders (they are not part of the sequence that formed where it is now, but have been eroded from limestone beds some distance away to form boulders, and only then washed together to form the conglomerate bed at Andamooka after transportation in flowing water - so the limestone formed elsewhere and was brought there as boulders). Then the opal replaced it. This should make it clear. As I thought the overwhelming majority of opal at Andamooka does not replace limestone (I have been down a number of mines there). So - yes it occurs, no it does not dominate and we were both half correct.

"Opal at Andamooka occurs in the shallow marine Bulldog Shale, part of the Marree Subgroup of Early Cretaceous age, which overlies Algebuckina Sandstone or laps directly onto pre-Mesozoic rocks (Fig. 2). The top sub-unit of Bulldog Shale, calledkopi by the miners, consists of highly weathered white sandy clay with scattered, large erratic boulders. At the base of the kopi there is an extensive sandy boulder bed, called the concrete or conglomerate band, which contains numerous pebbles, cobbles and boulders of pre-Mesozoic rocks, chiefly Arcoona Quartzite. Beneath the conglomerate band is a pale brown, grey or yellow claystone with a low sand content referred to as the mud.

Opal at Andamooka occurs predominantly at one horizon, referred to by miners as the level, at the contact of the conglomerate band and the mud. Other sub-levels (squibby levels) occur above the main level but none are as prominent, continuous or productive.

The main opal varieties produced are crystal opal (transparent to translucent), white opal, and some black opal. Painted ladies are boulders, generally of quartzite, which split along a fracture to reveal a coating of opal. Matrix opal is cloudy stone with flashes of colour, which is thought to form by replacement of limestone boulders in the conglomerate band. Opalised sandstone or opalstone forms by deposition of opal in the spaces between the quartz grains in sandstone boulders. Both matrix and opal sandstone can be treated by soaking in sugar solution and boiling in sulphuric acid to darken the body colour and enhance the play of colour".

So now you have an accurate answer.....and the opal has probably already replaced any limestone so that there is none left to dissolve in acid. Hope that helps.

Attached is a photo I took of a "Painted Lady", a boulder coated with opal. We call boulders like this dropstones - they formed far away and were rafted on top of floating ice where glaciers met the Cretaceous sea, until the ice melted and they dropped far from shore and far from their source area. It was cold in the Cretaceous - you may have heard of the opal "pneapples" of White Cliffs - they replace ikaite crystals (a calcium carbonate mineral different to calcite). Today we only find ikaite crystals in the cold bottom muds of Norwegian fiords. Photo also shown of a White Cliffs "pineapple".

1488855149_painted_lady.jpg


1488855315_pineapple.jpg
 
Thank you very much for that info Goldierocks, it makes a lot more sense that the limestone was in the conglomerate and was replaced by the opal, than the opal forming in the limestone.
As i said it can get confusing sometimes when i get conflicting information, so its a huge help getting to the bottom of it.

I do understand the sugar solution is there to be converted to carbon. When i thought the Andamooka matrix was limestone, i again just assumed there must have been something protecting the calcium carbonate from the acid and all i could see was the sugar. So again this process makes more sense knowing its not a limestone matrix.

I have heard of opal being found in dropstones, but never seen it myself, as i had heard of opal pseudomorphs but never seen any before.
That White cliffs pineapple looks very interesting.
 

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