Geologists please

[Karls48]

This is question mostly for Carl (Renormalised) and any geologists or opal miners in this forum. Long long time ago when there were no speed limits, no RBT, no political correctness, when you could drive around with your Ute loaded with Gelignite, Nitro Phil, Cordex, detonators and fuse, when you could walk in Pub with your rifle and have beer without rising anyone’s eyebrow I was mining for opals in Coober Pedy. That was the time when throwing a stick of Gelignite with lighted fuse (without the detonator) in Pub’s Bar was consider “funny”. That was the time when Melbourne Mafia used to track Moonshine in to Coober Pedy in 2000l trailers disguised as fire tenders. That was the time when local police force amounting to two if I remember correctly used to lock up all drunken Abos (native Australians) and send them next morning to do noodling. Because of incredible eyesight or ability to spot difference of native Australians Police Sergeant finished up with nice purse of opals in exchange for smokes, beer and freedom.
Anyhow, enough rambling about past and long gone by. My question is - old timers used to say – when your drive (horizontal tunnel blasted and dug from your vertical shaft) intersect the Slide(kind of rusty brown line running thru white sandstone – I think minor fault line) you will find opal on other side. Is there any justification for this?

[Kevnool]

At White Cliffs in NSW they go down there shafts then they dig there drives only when they find layer rocks (Which are at the bottom of old creek beds) in the sediment and thats what the drives follow that very thin sedimentary layer.

Cheers Kev.

[renormalised]

Opals will and do occur along faults and cracks in the rock, where water has had time to percolate through it carrying dissolved silica. Once the water gathers in a spot and allows the silica (in a colloidal gel form) to precipitate, you'll eventually get opal. The rusty colouration in the rock is just that, rust (iron oxide). With the sandstone, the natural porosity of the rock allows silica rich water (usually slightly acidic) to percolate through the pores and deposit opals in the surrounding rock as well. Over time, you'll get a band of opal replace the sandstone on either side of the fault line/crack.

[renormalised]

That's right, Kev....they're following the sandy seds on the old creek and gully bottoms that have been infilled with gravel and dirt over the years. The silica comes from rainwater percolating down through this overburden and then it gets trapped in the sed layers in the old creeks.

[Baddad]

Hi Carl and Others,
Opal contains water and it is affected by water. That is why women wearing on opal ring need to take it off before washing dishes.

It can affect the opal quality.

Cheers

[Octane]

I find it rather amusing that you would type such a lengthy post, but, couldn't spell "Aboriginals"; preferring to refer to them by a derogatory term; and, then qualifying the term with "native Australians".

H

[Karls48]

So old timers were right. There is better chance for opal in proximity of "Slide".
Although it did not work for me - I did found chunk of potch size of house brick near the Slide. Also a rock (jasper I think) about half of brick size encrusted in potch and milky opal

[renormalised]

That's right:)

[renormalised]

Did you try and crack it open. Sometimes potch contains good opal. Lots of people find lumps of potch and just throw it away thinking it's no good. Some people have had small fortunes in their hands without realising it!!!.

My experience with gems and such not only comes with being a geologist, but I've also been prospecting for gems and such since I was knee high to a grasshopper:) Found my first sapphire when I was about 2:):) Could grade them according to colour and quality when I was 5:):)

[Karls48]

I used term that was used in that time. I did not invented that term, it was used by everyone in those times. What you want me to do - wipe out history so you can feel OK?

[AstralTraveller]

Karl,

Technically speaking you don't want a geologist, you want a soil scientist. That stuff you dug through is a deeply-weathered soil profile, not a rock. The parent rock has been weathered (chemically altered) but not eroded (transported). The process has gone over about 60 million years (give or take) which surely makes it one of oldest such formations on Earth.

[Octane]

A little respect never hurt anyone. It's 2012, not the 60s or 70s.

H

[Karls48]

No I did not. But you are right, I should have. In those days potch and milky opal was worthless - now you can get some money for it because Chinese are making all sorts of ornaments from it. But when we went to try our luck
to Duck Creek in Queensland that was another story. The field got (boulder
?) opal and we used to broke every nodule we found.

[renormalised]

Pretty much the majority of the continent has undergone that process...in situ weathering and lateritisation, especially up north here. The main reason why you have the bauxite deposits at Weipa....also where you get really nice rhodochrosite :):)

[Karls48]

60s and 70s did exist. I spend more time in bush living, working, drinking and fighting with Aboriginals then you did living in big smoke. I can still recall few word of the language spoken by them around Coober Pedy. What do you want?
To change history of Australia? Respect - I got more respect for them then people that got their "respect" from TV documentaries.

[AstralTraveller]

In 2007 the International Quaternary Association congress was held in Cairns and before and after the congress field trips to various places of (scientific mostly ;)) interest in Oz and NZ were run. I drove the minibus for my boss's field trip from Adelaide to Alice via (amongst other places) Coober Pedy. Apart from one South African they were all from the northern hemisphere, where the soils have mostly been stripped by glaciers and none are more than 15,000 years old. I realised my boss was being 'subversive' by bringing them to a place which was so different to anything they had seen where all their 'types' and pidgeon-holes didn't work. One young German scientist who was on some commission or other about soil classification asked my boss how he would classify the soils, to which he replied to the effect that he didn't try to classify, just explain the process of formation.

[Karls48]

As far I know there is no need to remove your opal ring when washing dishes.
Provided that your stone is solid opal and you are careful not to scratch it. Lot of opal jewellery is made from doublets and mostly from triplets. Opal triplet consist of darkish potch back, with very thin slice of good opal glued to it and quarts top lens glued on top.
It got many advantages. It looks good and comparing to solid stone - it is scratch resistant. Opal is fairly soft stone about 6 (I stand corrected if someone comes up with correct hardness) against the diamond at 10 and sapphire or ruby at 9. So it scratch easily. Triplet does not surfer from scratching but when immersed in water it can de laminate.

[Baddad]

Hi Karl,
MOHR hardness scale for opal: 5.5 to 6.5. So your figure was correct.

Sudden temperature changes of cold water to hot etc can crack the opal.
I have seen an opal become milky grey over years of the woman never taking the ring off when washing dishes. This was back in the early 60's. The discolouration was minor but certainly present. I'm not aware if it was delaminating or solid, as I was not aware of such things then.
Cheers

[casstony]

All of the aboriginals I went to school with in Orbost were decent kids. I remember a few nasty white bullies but I never had a single problem with any of the aboriginals.

Tarring a whole people with the same derogatory brush is neither polite or sensible.

[Allan_L]

I am sure Karl meant no disrespect.
At least that's how I read it.
If you disagree, use the "report this thread" option rather than stir open conflict.
Lets keep on topic, less more threads be closed down.

I apologise in advance if my words are construed so as to cause anyone offence.

[casstony]

Hi Allan, I did use the "report this thread" option but apparently the moderators do not find the term "drunken Abos" to be offensive, so I felt compelled to publicly defend the good people in the aboriginal community.

Regards,
Tony

[Karls48]

I beg your pardon. It may be that I can't write in English (I'm wog you see) but then it seems that you can't understand it. This thread is about opal and I simply described conditions in Coober Peddy at time when I was mining for it Nowhere I wrote anything bad about Aboriginals.

[casstony]

Then stick to talking about opals and leave out the term "drunken abos".

[Karls48]

Please replace with - Intoxicated Aborigines.