It is with great sadness I'd like to announce Dr. Hanneman passed away on December 12, 2020. His legacy will live on forever!
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 Post subject: Re: In need of Help Identifying...
PostPosted: Wed Jun 08, 2011 5:51 am 
Barbra Voltaire wrote:
....This article on Observations of Treated Feldspar by Shane McClure addresses the issue of what appears to be a color change in diffused plagioclase:


Thanks for the link to that very useful paper, Barbra. It confirms and explains what I have recorded as present in my own sample. Bought as 'From Tibet' naturally :P But at a modest enough price to be worth acquiring out of curiosity.

I would not have thought to describe (in my stone) the occasional appearance of some green colouration as 'colour change' though, since its appearance is patchy, seeming more of a 'colour flash', very dependent on light positioning. Never seen 'in the hand' either, in this small stone, but only under the microscope. It's good to know that Jason and others have often found otherwise.


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 Post subject: Re: In need of Help Identifying...
PostPosted: Wed Jun 08, 2011 10:19 am 
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Kerensky wrote:
If you can get your hands on a copy of the latest edition of 'Gems' (Ed. M.O'Donoghue 2006), You will find a quite thorough treatment of the Plagioclase Feldspar series Albite-Anorthite. In particular, the details given in p 245-247 re. RI and SG are quite thought provoking I find.


Hi Owen....I don't have the latest Gems. Can you describe the nature of the treatments covered on p 245-247.
Thanks.

Allanotaylor, if you have an interest in the andesine/labradorite treatment debacle which has transpired over the last decade, I'll send you some additional info. :D
Let me know.


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 Post subject: Re: In need of Help Identifying...
PostPosted: Wed Jun 08, 2011 12:14 pm 
Barbra Voltaire wrote:
Kerensky wrote:
If you can get your hands on a copy of the latest edition of 'Gems' (Ed. M.O'Donoghue 2006), You will find a quite thorough treatment of the Plagioclase Feldspar series Albite-Anorthite. In particular, the details given in p 245-247 re. RI and SG are quite thought provoking I find.


Hi Owen....I don't have the latest Gems. Can you describe the nature of the treatments covered on p 245-247.
Thanks.


The information in those pages, is graphic and tabular, the text providing a framework and giving certain additional information regarding the accuracy of the data. The info is as follows:

1. An X-Y graph. The x axis is graduated in the molecular percent of Anorthite from 0 - 100 (i.e. from Na 0% to Ca 100%. On the y axis there are left and right hand scales. Left gives RI and right gives SG. On this are drawn the lines for changes in SG and alpha, beta and gamma ray RIs, as the mol % of Anorthite in a Plagioclase crystal increases. The key info to be extracted is:
[tab] a. The increases in beta RI and in SG are both linear, rising with mol% Anorthite in the sample content[/tab]
[tab] b. The rise in RI for the alpha and gamma rays is non-linear. Both lines having a kink in them. For the gamma ray, the kink is at approx mol% 26 and at mol% 60 for the alpha ray.[/tab]

2. A bar chart, setting out how the optic sign and varietal names change as the Anorthite mol% in the Plagioclase series increases. This chart shows that:
[tab] a. The optic sign of the Plagioclase series changes pos - neg - pos - neg as the Anorthite % content rises.[/tab]
[tab] b. The three pos/neg switch points are not linearly spaced with the rise in Anorthite mol%. [/tab]
[tab] c. These optic sign switchpoints do not co-incide with the arbitrary mol% limits set for varietal differentiation in the Plagioclase series Albite - Oligoclase - Andesine - Labradorite - Bytownite - Anorthite. I.e. Two of the switchpoints occur at some Anorthite mol% point within the varieties Oligoclase and Andesine. The third switchpoint occurs at or close to the arbitrary Andesine/Labradorite mol% boundary. [/tab]
[tab] d. The arbitrary mol% Anorthite division of the series beween the six varietal members is given in a useful isomorphous replacement chart on p. 243 and is repeated in the write-ups for each of the varieties elsewhere in the Feldspar group chapter. [/tab]

Sadly, neither the chapter author, Brian Jackson, nor the editor, M.O'D, cite a primary source for any of the above very interesting information. If anyone here knows the primary source(s) for it, I'd be really glad to know.

Good stuff continues for Plagioclase series and Alkali Feldspars with tables (attributed to webminerals.com) of the RI and birefringence for each variety. There are also tables (unattributed) for the varietal SGs.


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 Post subject: Re: In need of Help Identifying...
PostPosted: Wed Jun 08, 2011 1:28 pm 
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allanotaylor wrote:
Barbra is right.. you cant do much from just a photo.
However, you can gain some useful info by just playing around with it.
Check out the most likely possibility, which is an "alexandrite" type synthetic corundum.
Find amongst your collection of gems a known synthetic corundum and compare the optical properties.
If you don't have a refractometer try comparing the optical properties when imersed in a liquid, such as cooking oil.
My Helium article "How to identify a loose gemstone" may help at http://www.helium.com/items/2104650-gem-testing-today
Cheers
Allano



Hi! Allano,


Thanks for all your feedback on helping me try to identify this mystery gem. After playing around with it and doing a-little more research I decided to take your advice from the article you written and do a cooking oil test. I submerged three stones in cooking oil to compare (just for fun, to learn a bit and experience a new technique). Out of the three I know for sure one was Smokey Quartz, the other Blue Topaz, and the third was the green color change stone in question. I attached some pictures so you can see the image the gems produced on white paper and their black boundaries. After the research I’ve done and seeing the narrow black boundary from the oil test I probably even though I’ll hate to admit it would say that this stone is treated green andesine/labradorite :smt022 . However, I still can’t make a final conclusion. ](*,) I am just not an expert gemologist. I just did this test as an experiment to see the black boundaries and compare the color change mystery gem to the known ones I have. I am sending this stone out to a lab for further analysis. I may take some time (months) but, I thought you guys could use an update and this is the best update I can give for now. Thanks again for all your help.

Rich



Image
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 Post subject: Re: In need of Help Identifying...
PostPosted: Thu Jun 09, 2011 11:30 pm 
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You should get it tested. Also check for a rock and mineral club in your area, many of them have Gemologists as members who may give you an ID for little to no cost.

But seeing the immersion and just the appearance of the stone after handling a few hundred carats of these stones they tend to jump out at ya, lol, I have to agree with Jason on his guess. It does appear, from what can be seen, to be the diffusion treated andesine-labradorite. Especially when you say from an old parcel, I am guessing you mean a parcel from a TV show? But it just can not be confirmed from a picture, sorry.

Do you happen to have a carat scale? If so have you tried a simple hydrostatic specific gravity rig?

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 Post subject: Re: In need of Help Identifying...
PostPosted: Thu Jun 09, 2011 11:59 pm 
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Swishman wrote:
You should get it tested. Also check for a rock and mineral club in your area, many of them have Gemologists as members who may give you an ID for little to no cost.

But seeing the immersion and just the appearance of the stone after handling a few hundred carats of these stones they tend to jump out at ya, lol, I have to agree with Jason on his guess. It does appear, from what can be seen, to be the diffusion treated andesine-labradorite. Especially when you say from an old parcel, I am guessing you mean a parcel from a TV show? But it just can not be confirmed from a picture, sorry.

Do you happen to have a carat scale? If so have you tried a simple hydrostatic specific gravity rig?



Hi thanks for all your advise. I do have a carat scale and have not tried the hydrostatic specific rig, how would youo go about doing that?


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 Post subject: Re: In need of Help Identifying...
PostPosted: Fri Jun 10, 2011 12:33 am 
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 Post subject: Re: In need of Help Identifying...
PostPosted: Fri Jun 10, 2011 6:33 am 
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Hi Kerensky
Thanks for that info re the latest edition of "Gems" and data about andesine etc. My copy of Gems is pretty ancient but still useful for the basics. Since this topic has come up I have browsed the internet and find on the http://www.gemselect.com dealer website many faceted andesines for sale plus side comments about the material. Very interesting. It is amazing what obscure (? unusual) gem material is on the market. (including pollucite... Tim)
Cheers
Allan


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 Post subject: Re: In need of Help Identifying...
PostPosted: Fri Jun 10, 2011 2:24 pm 
allanotaylor wrote:
Hi Kerensky
Thanks for that info re the latest edition of "Gems" and data about andesine etc. My copy of Gems is pretty ancient but still useful for the basics. Since this topic has come up I have browsed the internet and find on the http://www.gemselect.com dealer website many faceted andesines for sale plus side comments about the material. Very interesting. It is amazing what obscure (? unusual) gem material is on the market. (including pollucite... Tim)
Cheers
Allan


You're welcome Allan.

Shortly after I signed up here, I asked which edition of 'Gems' it would be best to buy. Bill Hanneman suggested that I buy both the 6th (newest and a substantial part-rewrite) and the 3rd, the last for which Robert Webster had full responsibility. I took that advice and have been glad ever since that I took Bill's advice.

Perhaps because Webster's name awas finally dropped fromn the cover, along with an excision of a deal of his writings and with the introduction of much new stuff, even last year many were still curling their lip at M.O'D's 6th edn with the result that I could buy one new and discounted, plus a s/h 3rd edn in good nick for less than I would have had to pay for a v.g. s/h copy of the 5th edn, revised and edited by Peter Read in 1994. Last time I looked, the 6th edn was three times the price I paid for it last year and, presently, I get spammed by Amazon, monthly, asking if I'm bored with it yet and would like to sell it back to them :lol:

Not that the 6th edn is perfect.... The indexing is in need of drastic improvement; footnoting is almost non-existent, some of the stuff carried forward from earlier editions is in need of titivating - e.g. who talks in Angstroms, these days? - and the main SG table is in a typographical mess which a proof reader should have picked up at the galley stage. That said, it's my daily companion and the 3rd edn is read for pleasure and occasional cross checking.

Owen


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 Post subject: Re: In need of Help Identifying...
PostPosted: Fri Jun 10, 2011 6:05 pm 
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Hi Owen (aka Kerensky)
Thanks for your info about the various editions of Websters 2 vol book on "Gems"
Its amazing what happens in gemology if you leave off following it for 25 years.
You have made my day, for on inspection of my well kept 2 vol, hard cover "Gems" I see that it is a 1st edition,
1962, and that I bought it in USA in 1964.
Reference to the 2nd hand book website http://www.abebooks.com shows that 1962, 2 vol set, ex library, sell for $100, and some booksellers in Canada and USA want $200 to $250 for it as a collectable.
I must continue to take good care of it as it is now a family heirloom, worth more than most of my gemstones.
Cheers
Allano


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 Post subject: Re: In need of Help Identifying...
PostPosted: Fri Jun 10, 2011 7:55 pm 
allanotaylor wrote:
...Its amazing what happens in gemology if you leave off following it for 25 years.


I can imagine.

Quote:
You have made my day, for on inspection of my well kept 2 vol, hard cover "Gems" I see that it is a 1st edition,
1962, and that I bought it in USA in 1964.
Reference to the 2nd hand book website http://www.abebooks.com shows that 1962, 2 vol set, ex library, sell for $100, and some booksellers in Canada and USA want $200 to $250 for it as a collectable.
I must continue to take good care of it as it is now a family heirloom, worth more than most of my gemstones.


Lucky you! First edition eh? It can only keep on increasing in value now.

Webster's last personal edn, the 3rd, was published in 1975 and, even since then, the gemmology rocket has travelled far. What with the addition of new gems to the marketplace and, most particularly, the explosion in the range and sophistication of gem treatments, imitants and synthetics the gemmo world is much changed. The 2006 6th edition has 31 chapters, of which 14 are completely fresh work by contributing authors who are specialists in the topics covered (e.g. Richard Hughes wrote the chapter on Ruby and Sapphire). The two chapters on Garnet and Feldspar respectively are both written by Brian Jackson in such a lucid fashion as to make the ins and out of solid solution series (in the case of Garnet, with three or four competing proposals to rationalise the grouping and nomenclature and all since 1980) seem comprehensible even to a newcomer. Even the remaining 17 chapters are heavily revised or replaced by Mike O'Donoghue, who made his reputation with his earlier works on synthetic gems and, in addition to his overall revision of writing retained from earlier editions, there are whole new sections by him, dealing with the man-made and manipulated materials.

All that said, books, however good as works of reference, of necessity lag somewhere between 3 - 10 years behind 'where it's at'. I think that only by constant updating through ingesting the leading trade and academic papers in the field, symposia, personal research etc. can the professional stay in sight of the cutting edge.... The books are fine for the likes of me though, who come to gemmology from a standing start. We all start somewhere.... :wink:


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