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avatar Re: Amphibole Group
March 06, 2012 08:38PM
    
Great Work Olav!!!

I had a look at the 2006 Can Min paper of Hawthorne and Oberti on Amphibole classification which for some reason is not posted at RRUFF. Can Min has been very good letting Bob post articles and Bob has done a tremendous amount of work posting what is at RRUFF. Anyway the two extreme classificaton schemes are most interesting. The second possibility which would eliminate Richterite and Pargasite, as well as others, is supposed to cleave to the IMA's predilection for dominant lattice sites being used to define species. While I'm all in favour of eliminating names in general, I find this supporting argument a little hollow since the different lattice sites are already lumped into 5 "sites" for the general formula. The competing interests of collectors, crystallographers and petrologists make this an almost impossible task.

I asked Tom Moore at Min Rec about the winchite ref and here is his reply:
“…the published reference to it was made in vol. 36 no. 3 (May-June 2005), p. 294. No, it had not been verified. That's because this "reference" is only a passing paragraph in my report on the 2005 Tucson show. As part of my description of the then-new sodalites from Sar-e-Sang I wrote "A few years back, equant crystals of sodalite to several centimeters, with winchite in marble, made a dramatic appearance on the western market..." The "few years back" was my report on the 2001 Denver Show in the issue of Jan.-Feb. 2002, wherein, talking about the new "hackmanite" specimens from Sar-e-Sang, I wrote that the hackmanite crystals "..are embedded, not in the white marble we'd expect, but in yellowish brownish white groundmasses of an amphibole called winchite, with large, tabular glassy crystals of the winchite surrounding the hackmanite crystals." So you see, these "references" are in no technical way authoritative; they only represent things that dealers-- primarily Dudley-- told me in the midst of shows, as I interrogated them in order to gather material for my show reports. Which of course leaves the mineralogy of these things just as open to question, and in need of expert verification, as ever.“

I also asked Dudley Blauwet and he replied:
": Herb gave Peter Levin's, a qualified mineralogist, a piece of the amphibole to check. Herb told me that Peter had checked it when I asked if he had checked out the yellow mineral. I went with that id [Winchite] as there was no other one available at the time, and Peter is a good mineralogist. When I met Frank at either Denver or Tucson after the Peter Id, I felt that Frank would be the best to check the amphibole again as it is notorious for being difficult to correctly analyze. He wrote me back shortly thereafter, and came up with Potassian Fluorian Richterite, and since then I have used that label or simply shortened it to richterite, and then told people that it was potassian fluorian if they asked, so that is the story, and knowing that Frank is the world expert on amphiboles, I have accepted his as the correct ID.

Potassian Fluorian Richterite (Richterite with signifcant, but not dominant K and F) is exactly what RRUFF found: [rruff.info]
Notice that the Fluororichterite posterd at RRUFF (http://rruff.info/fluororichterite/display=default/R060290) and supplied by Herb has been identified by XRD only. I'd be happier with this ID if it was supported by good probe data like the richterite.

The deposit is small and no more has since appeared. The specimens appear to have a homogeneous mineralogy, so while Richterite is definitely there, it seems unlikely that Fluororichterite or Fluoro-patassicrichterite are present as well. It is so expensive and difficult to analyse these things, that if these were present they would probably be passed unnoticed.

My 2 cents is that Mindat should call these Richterite, pending further analysis.



Edited 2 time(s). Last edit at 03/07/2012 07:08PM by Rob Woodside.
Re: Amphibole Group
March 07, 2012 12:32AM
    
So I guess I don't have winchite although I winch I did!



Edited 1 time(s). Last edit at 03/07/2012 12:34AM by Reiner Mielke.
Re: Amphibole Group
March 07, 2012 12:05PM
    
Rob,

Thank you very much both for your encouragement and for your help in "sorting out" the richterite/winchite issue. Thanks smiling smiley

I agree that the winchite images should be moved to the richterite gallery. As you say, this is a limited find in a very special geochemical environment, and although the K/Na and F/OH ratios is variable, the high overall alkali content (and low Al in the analysed amphibole) seems to indicate that winchite is an unlikely candidate.

I have studied the 2006 paper with some interest. I am not sure that randomly (i.e B position Na/Ca >1 or <1) naming these and other richterites for either Al-deficient edenites or Al-deficient eckermannites will really solve any problems. My take on this is that the classifications and naming conventions of the amphiboles have been in more or less constant revision since the 1960-ties and I don't see it end quite yet, even if a new neming convention is underway.

From my perspective, I'd rather map things as good as possible according to todays system and from there make the neccesary corrections when something new is agreed upon, rather than sit and wait.

Olav
Re: Amphibole Group- Winchite definition
March 20, 2012 08:04PM
    
I struggle to understand why winchite is defined as it is. The chemical formula reads ☐( NaCa) (Mg4Al)Si8O22(OH)2, yet Leake et. al (1997) defines an amphibole as winchite if the following conditions are met:

1 (Na+K)A<0,5 apfu
2 (Na+Ca)B>1
3 0,5<NaB<1,5 and
4 SiT>7,5

There are no requirements to the Al content, which I find strange taking the formula into consideration.

As a result of this definition, the following amphibole from Långban, Sweden is classified as winchite, even if it contains almost no Al at all:

(Na0,254,K0,112)0,366(Na0,579,Ca1,320)2(Mg4,823,Mn0,278)5,001(Si7,898,Al0,059)7,987(OH)2,182F0,159

To me this looks more than anything like an intermediate composition between tremolite and richterite.

Why is this a winchite rather than a tremolite with a high richterite component? What is it that I don't get here?

best regards

Olav
avatar Re: Amphibole Group- Winchite definition
March 20, 2012 09:48PM
Olaf, don't worry, not many of us understand the amphiboles. Winchite, like many amphibole names, is an unnecessary name for an intermediate composition between well defined end members, in this case tremolite and glaucophane. Though in your case there are significant components of other end members such as eckermannite and a Mn rich end member. Hawthorne and Oberti (2007) suggested getting rid of these intermediates, but there does not appear to be any agreement on this, sadly.

The analysis does fit the current rules for winchite, Al and Fe3+ are unnecessary, despite being usually shown in the formula for charge balance, but your analysis has unusually high Na/(Al+Fe). Under the new classification by Hawthorne and Oberti (2007) it would simply be a sodium-rich tremolite.

Regards,
Ralph
Re: Amphibole Group
March 21, 2012 11:20AM
    
Ralph,

Thank you for your reply. smiling smiley

I fully agree that the winchite-series seems quite unnecessary, and that it should at some stage be discontinued. These minerals are however still considered valid. I also agree with you that a Na and Mn rich tremolite seems like the natural ID for the above amphibole .

Winchite from the type locality ( yes I know that's a complex story in it's own right) has approximately 1 apfu (Fe 3+,Al), thus corresponding with the approved formula, which again corresponds with the concept of winchite as being intermediate between tremolite and glaucophane.

The analysis referenced above is published as Winchite in "Rock Forming minerals" and that this spreadsheet also name this amphibole as winchite.

What puzzles me is that it is OK to just ignore one of the components in the chemical formula ( in this case Al in the C position) when assigning an ID to a mineral. I know there are good reasons for doing this, and that nobody really cares that much, but it contradicts several of the other principles for identifying minerals, and it obscures the possibilities to ID amphiboles for "normal" people.

Olav



Olav
Winchite Praborna Mine, Italy
March 22, 2012 09:47AM
    
This specimen:

Winchite 12mmx1mm in 35mm specimen©


seems to fit better with the description of richterite from this locality: "The richterite-series minerals occurs in the braunite/quartz ore zone as fibrous yellow-brown bundles and fans or as elongated pink crystals in fracture zones" than the description of winchite from the same locality: "In classical metabasalts, Ca–Na amphibole corresponds to barroisite whereas winchite is prevalent in hydrothermalized magnesian metabasalts.".

I know that these short descriptions are not at all sufficient confirm/disapprove the ID of this amphibole, that's why I post this here rather than in the Mistakes and Errors section. I still think it would be fair to say that based on available literature, the occurance of winchite within a quartz vein is "untypical" for the locality.

Olav
avatar Re: Amphibole Group
March 24, 2012 11:40AM
Olaf, the definitions of the amphiboles should rely on the compositional limits given by Leake et al, not the formulae given, which are just a summary indicating typical compositions. A more comprehensive formula for winchite would be (Na,Ca)2(Mg,Fe,Al)5Si8O22(OH,F)2

Regards,
Ralph
Re: Amphibole Group
March 27, 2012 08:33AM
    
Ralph,

Thank you for taking the time to explain this smiling smiley

Olav
Re: Amphibole Group-taramite-brazil
April 03, 2012 08:08AM
    
There are two photos showing large bladed aggregates of taramite from Itinga, Minas Gerais Brazil in the photo gallery: Taramite gallery.

Given the rarity of this mineral and the geology of the area, these specimens are almost too good to be true ( for a rare amphibole that is). Can anyone familiar with the area confirm these as taramites?

Olav
avatar Re: Amphibole Group-taramite-brazil
April 03, 2012 09:17AM
You might want to contact Luiz, our Brazil expert. He may be able to say yes or no. Failing any sort of a definite yes or no from him, you can always consult the user directory and contact the uploaded and ask him/her directly about the ID of the specimen in the images.

Rock Currier
Crystals not pistols.
Re: Amphibole Group-taramite-brazil
April 03, 2012 12:14PM
I suspect that those are black kyanites, and not an amphibole at all!
Re: Amphibole Group-taramite-brazil
April 04, 2012 05:34AM
    
Thanks guys,

I've sent Luiz a PM

Olav
Amphiboles from the Quincy Granite, Mass. USA
May 22, 2012 07:11PM
    
The alkaline Quincy and Cap Ann alkaline granites hosts several locality entries in Mindat in Quincy, Rockport and Gloucester (+ others?).

I know there are many knowledgable Mindaters on the US East Coast. I will really appreciate if anyone can share any additional information, thoughts and/or input to the following statements:

In Mindat, the following amphiboles are listed from these alkaline granites without (in my mind) sufficient analytical support justifying the entry in the database:

- Katophorite from the Quincy granite, ref Emerson (1917). As I interpret Emerson's text, he is referring to the green hastingsite from the Cape Ann granite when he is describing the "katophorite"

- Arvfedsonite from the Quincy granite, ref Sayer (1974). Sayer refers to the blueish amphibole in these alkaline granites as riebeckite-arfvedsonite without any analytical data supporting the occurance of arfvedsonite in the Quincy granite.

- Magnesioriebeckite-riebeckite series var crocidolite. The riebeckite from all these alkaline granites are very poor in Mg. The analysis show a MgO content from "not detected" to 0,32%wt, including the crocidolite variety. I think listing this as part of a series is somewhat misleading.

I base this on analysis published by Lyons (1972), Lyons(1976) and Warren & Palache (1911) these granites contains amphiboles of riebeckite and hastingsite composition in that the Quincy granite contains only riebeckite and the Cape Ann (and Peabody ) granite carries greenish hastingsite as it's main amphibole, and the bluish amphibole is a arfvedsonitic riebeckite with a higher Na content (+/- 7,5%NaO) than the Quincy granite ( 6-6,25%), but still with NaA<0,5.

The full references are:

Charles H. Warren and Charles Palache(1911): The Pegmatites of the Riebeckite-Aegirite Granite of Quincy, Mass., U. S. A.; Their Structure, Minerals, and Origin, Proceedings of the American Academy of Arts and Sciences, Vol. 47, No. 4 pp. 125-168

BK Emerson (1917): The geology of Massachussetts and Rhode Island, USGS Bulletin 597

Paul C. Lyons (1972): Significance of riebeckite and ferrohastingsite in microperthite granites, Am. Min Vol. 57, pp.

Sayer, Susan (1974): An Integrated Study of the Blue Hills Porphyry and Related Units, Quincy and Milton, Massachusetts (MIT master's thesis)

Paul C. Lyons (1976): The chemistry of riebeckites of Massachusetts and Rhode Island, Min. Mag Vol 40, pp 473-479

Btw- I have pdf's of all the listed references, and if anyone is interested, send me a PM and I will e-mail the pdf(s).

Olav
avatar Re: Amphibole Group
May 22, 2012 09:51PM
    
Hi Olav,

Unfortunately, when "crocidolite" is entered on Mindat as a species, the listing defaults to "magnesioriebeckite-riebeckite series var crocidolite." You are correct that the Quincy (and Cape Ann = Rockport/Gloucester) "crocidolite" is riebeckite. These amphiboles and their host granites are extremely low in magnesium.



Edited 1 time(s). Last edit at 05/22/2012 09:54PM by Peter Cristofono.
Re: Amphibole Group
May 22, 2012 11:02PM
Peter, since it is known that these crocidolites at this location are riebeckite, then the simplest solution would be to relabel the 2 Quincy "crocidolite" photos as "Riebeckite" and just note in the caption that they are the crocidolite variety.
Glaucophane Italy
June 15, 2012 05:02PM
    
I am currently writing the "Best Mineral" Article on Glaucophane. The Western Italian Alps are one of the core areas where this mineral is found. Being a mineral formed at High and Ultra High pressures at relatively moderate temperatures, it is predominantly found in schists and eclogites as a rock forming mineral.

I have found an extensive suite of literature describing the geology, the localities, petrology and mineralogy of this terrane in Italy. The one thing that puzzles me, and that are not described anywhere are the photo's uploaded to Mindat of free-growing glaucophane crystals like these:

Glaucophane 2mm FOV © C.Boutry
Glaucophane © Jasun McAvoy


As these rocks are generally not vuggy, I wonder if anyone can share information on how these fre-growing glaucophanes occure, wether in vugs or by removal of some other minerals (talc or other) to free the glaucophane. I will appreciate any infromation.

Thanks

Olav
Re: Glaucophane Italy
June 25, 2012 08:51PM
I suppose they are etched out of calcite (or aragonite).
Re: Amphibole Group
September 05, 2014 10:39AM
Hello All.

"Long time listener, First time caller" grinning smiley

First of all, being an (amateur) amphibole aficionado, let me say thumbs up.

Bart/Reiner - your comments summed it up nicely – amphibole nomenclature, in my opinion, has gotten way out of control. But, it is what it is (unless someone is willing to go head-to-head with the IMA smiling smiley).

Olav: if you're still working on this and would like any assistance, I would like to offer (as limited as it may be) any help I can on the analysis end of it - I am, in no way, an expert, but I do have to keep up on amphibole classification (occupational hazardsmiling smiley).

Regards
Frank
Re: Amphibole Group
September 05, 2014 11:36AM
Okay - My Bad (I just now "read" the rest of these):

Olav: I do have a comment on the Taramite (from Brazil). Perhaps a similar situation - I purchased a "very large" spray of bladed taramite, dark brown to black, from ???? (I have a photo of it that I will attach later today). The sample was only about 1.7cm by 1cm by .5 cm, but for taramite, that is huge (first red flag). But it was labelled taramite from a well known, respected collector, so I bought it (worth the risk!). Well, it wasn't taramite, it was kyanite. I suspect the locality is incorrect as well.

Not saying that what is posted is incorrect - will never know for sure without analysis smiling smiley

Frank

Kyanite - Nuovo Ritovamento, C.S.S.R.




Edited 1 time(s). Last edit at 09/06/2014 12:36AM by Frank Craig.
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