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Identity HelpUnknown alteration from Kipawa,Quebec

4th Dec 2018 20:43 UTCReiner Mielke Expert

I shouldn't be asking this but thought it might be fun to see what comes of it.

The sample is from here:https://www.mindat.org/loc-614.html

It appears to be a layer of brown Hiortdahite II in eudialyte with a white alteration layer on top. The white mineral looks somewhat fibrous but it difficult to tell as it is so fine grained. The white unknown is soft <3 but it is not possible to say if that is due to the cohesion of the fibrous crystals or the crystals. The thickness of the white layer is 2-3mm and the unaltered Hiortdahlite II layer 0.5-1cm. The white layer fluoresces pale turquoise under LW and the Hiortdahlite II layer reddish pink.

Here are some photos:

4th Dec 2018 20:53 UTCReiner Mielke Expert

More pictures and EDS results, the last EDS is of a Hiortdahlite II sample posted by Pavel on Mindat for comparison. My sample appears to lack Na but the system used under reports Na ( and over reports Ca) . It is possible that it contains no sodium in which case I do not know what it is. However it's fluorescent response is typical for hiortdahite II from there.

4th Dec 2018 20:53 UTCPaul Brandes 🌟 Manager

Have you had it analysed yet, Reiner?

Edit: strike the above comment! ;-)

4th Dec 2018 21:02 UTCRichard Gunter Expert

Hi Reiner:

It may be a mixture of gittinsite and another phase. Gittinsite is a white alteration product and your "unaltered" trace has calcium-zirconium-silicon which is should. The fluorescence of gittinsite at Strange Lake is bright orange in SW but I don't know what it is at Kipawa.

4th Dec 2018 22:28 UTCReiner Mielke Expert

Gittinsite certainly seems to be the most likely thing.

5th Dec 2018 20:28 UTCPavel Kartashov Manager

Zr:Si ratio in the alteration product is higher than in both zircon or gittinsite. And Ca peaks are too low for gittinsite also.

I am suppose here mixture at least of three phases, one of which is some calcian zeolite. Two other are zircon and free zirconia (may be ZrO₂*nH₂O).

5th Dec 2018 23:32 UTCReiner Mielke Expert

You are correct Pavel, Ca is much too low for gittinsite. I will dissolve some in acid and see what I get. If there is a zeolite it should dissolve. Actually the Zr:Si ratio of zircon Zr(SiO4) is 1:1 which this what this appears to be so that is a possibility. However I find it difficult to imagine zircon being an alteration product. Is free zirconia a mineral? I will also try a different hardness test by grinding some between two sheets of glass, If there is zircon it should scratch the glass.

5th Dec 2018 23:43 UTCAlfredo Petrov Manager

Remember that SEM/EDS isn't quantitative and is least quantitative for the light elements like Na, Si...

so I wouldn't trust that for determining Zr:Si

5th Dec 2018 23:50 UTCReiner Mielke Expert

It effervesced in HCl a little bit so the Ca is probably from calcite. Most of it does not appear to be soluble but it is too early to say for sure. Between two sheets of glass it easily turned to powder and I did not observe any scratches but that may be that it is so fine grained that I could not see the scratches. I will let you know what the final acid test results are. It looks like I will have to get powder XRD done on it.

5th Dec 2018 23:59 UTCRichard Gunter Expert

You might get baddeleyite (ZrO2) in there. At Strange Lake we did not get baddeleyite; the calcian elpidite altered to gittinsite and late-stage zircon. Unusually the late-stage zircon did not fluoresce in SW UV but the gittinsite did.

5th Dec 2018 23:59 UTCReiner Mielke Expert

Hello Alfredo

For two closely spaced peaks like that in that range it is close to the true ratio. There is only a problem when you are trying to compare peaks a relatively great distance apart, like the Si and Ca peaks. In this case Ca is greatly over reported so there is actually less Ca than the peak indicates. However like you say for light elements like Na there is a serious problem, in this case Na is grossly under reported and anything lighter than Na cannot even be detected with this setup. Either way I doubt I will be able to determine what this is without XRD. Also some of the Al may be contamination from the chamber so that cannot be quantified except to say ( because of the size of the peak) in this case Al is present.

6th Dec 2018 00:19 UTCPavel Kartashov Manager

Compare intensities of Si and Zr in EDX spectrum of zircon with your spectrum.

Remember that you should to extract some Si (approximately equal to Al) for zeolite. So Zr:Si ratio here in reality is even more than it is visible from the first sight.

6th Dec 2018 00:32 UTCReiner Mielke Expert

Hello Pavel,

I see what you mean but I do not know if Kerry's result is precise enough to rule out zircon. Here is an EDS by Kerry for zircon done a few years ago when he had a different detector so I don't know if it is directly comparable. However that pattern is similar to the unknown. I will get XRD done in a few weeks that should provide some answers.

6th Dec 2018 00:36 UTCPavel Kartashov Manager

Alfredo, when you constantly works with different zirconosilicates, you may approximately to recognize Zr:Si ratio (for example in row zircon-gittinsite/catapleyite-wadeite-elpidite).

Richard, you should to remember, that Strange Lake is granite, while Kipawa is nepheline-syenites with less abundance of silicon. Baddeleyite impossible in granite, but quite possible in syenites (especially alkaline and melanocratic).

I am think, that it don't manage without zeolite here, may be sodian.

6th Dec 2018 00:41 UTCPavel Kartashov Manager

Any analyst accustoms to his own detector... I unable to judge about one of Kerry. It looks like his detector understating Si systematically.

6th Dec 2018 00:48 UTCReiner Mielke Expert

Hello Pavel,

I agree that his old detector was under reporting Si. I do not know about his new one. I will ask him if he has results for Zircon that he got with his new detector.

6th Dec 2018 15:39 UTCRichard Gunter Expert

Hi Pavel:

I agree about baddeleyite at Strange Lake yet there was enough silica at both Strange Lake and Kipawa to form gittinsite.

7th Dec 2018 20:09 UTCReiner Mielke Expert

Except for a bit of carbonate the remainder is insoluble in HCl. Also Kerry's new detector gives the same results as his old one so it looks like his system favours Zr over Si.

13th Jan 2019 15:41 UTCReiner Mielke Expert

I had PXRD done on this material and it yielded no discernible peaks so I am assuming it is amorphous. My question is what to call it? Anyone have any suggestions?

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