Amphibole Group

Re: Glaucophane Italy

Erik Vercammen — Mon, 25 Jun 2012 20:51:52 +0000

I suppose they are etched out of calcite (or aragonite).

Glaucophane Italy

Olav Revheim — Fri, 15 Jun 2012 17:02:22 +0000

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: Amphibole Group

Alfredo Petrov — Tue, 22 May 2012 23:02:19 +0000

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.

Re: Amphibole Group

Peter Cristofono — Tue, 22 May 2012 21:51:57 +0000

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.

Amphiboles from the Quincy Granite, Mass. USA

Olav Revheim — Tue, 22 May 2012 19:11:28 +0000

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 Na^A<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

Re: Amphibole Group-taramite-brazil

Olav Revheim — Wed, 04 Apr 2012 05:34:15 +0000

Thanks guys,

I've sent Luiz a PM

Olav

Re: Amphibole Group-taramite-brazil

Alfredo Petrov — Tue, 03 Apr 2012 12:14:23 +0000

I suspect that those are black kyanites, and not an amphibole at all!

Re: Amphibole Group-taramite-brazil

Rock Currier — Tue, 03 Apr 2012 09:17:58 +0000

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.

Re: Amphibole Group-taramite-brazil

Olav Revheim — Tue, 03 Apr 2012 08:08:35 +0000

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

Re: Amphibole Group

Olav Revheim — Tue, 27 Mar 2012 08:33:25 +0000

Ralph,

Thank you for taking the time to explain this :-)

Olav

Re: Amphibole Group

Ralph Bottrill — Sat, 24 Mar 2012 11:40:33 +0000

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

Winchite Praborna Mine, Italy

Olav Revheim — Thu, 22 Mar 2012 09:47:55 +0000

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

Re: Amphibole Group

Olav Revheim — Wed, 21 Mar 2012 11:20:08 +0000

Ralph,

Thank you for your reply. :-)

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

Re: Amphibole Group- Winchite definition

Ralph Bottrill — Tue, 20 Mar 2012 21:48:49 +0000

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.

Re: Amphibole Group- Winchite definition

Olav Revheim — Tue, 20 Mar 2012 20:04:16 +0000

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 0,5B<1,5 and
4 Si_T>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:

(Na_0,254,K_0,112)_0,366(Na_0,579,Ca_1,320)₂(Mg_4,823,Mn_0,278)_5,001(Si_7,898,Al_0,059)_7,987(OH)_2,182F_0,159

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

Re: Amphibole Group

Olav Revheim — Wed, 07 Mar 2012 12:05:47 +0000

Rob,

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

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

Reiner Mielke — Wed, 07 Mar 2012 00:32:37 +0000

So I guess I don't have winchite although I winch I did!

Re: Amphibole Group

Rob Woodside — Tue, 06 Mar 2012 20:38:18 +0000

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.

Re: Holmquistite- Koktokay China

Jolyon & Katya Ralph — Tue, 06 Mar 2012 12:46:25 +0000

I'd say based on your research they should all be moved. If there are objections and there is analysis to back the objections, we can move them back.

jolyon

Holmquistite- Koktokay China

Olav Revheim — Tue, 06 Mar 2012 12:16:01 +0000

Holmquistite are known to occur in the Koktokay pegmatite field in China, and several photos are uploaded to Mindat. They are all similar to:


Holmquistite	© JSS

The issue is that one specimen acquired as holmquistite has been analaysed and the "holmquistite" turned out to be a tourmaline, see Mindat message board. The tourmaline looks like this:


tourmaline	© Donald Doell

Reviewing literature available on the net, such as Koktokay-tourmaline, Koktokay tourmaline and Koktokay-holmquistite indicates that "Holmquistite is a sky-blue to bluish mineral in the gabbro and gabbro -diorite country rock of Li-pegmatite, (being) brachyprismatic and acicular 0.5 -0.1mm or less in size" and that " Tourmaline occurs both in the contact zone and in
most of the internal textural zones of the pegmatite dyke in the cupola. Tourmaline crystals from the contact zone
and zones I to IV are black.....are distributed perpendicular to the contact wall, and their sizes can be up to 3 _ 10
mm."

To me these "holmquistites" seems questionable. I tried to e-mail one of the authors for a possible clarification, but I haven't yet received a response.

Should these photos be moved to the tourmaline gallery, or should they still be kept as holmquistite?

Olav

Re: Amphibole Group-Afghani winchite vs. richterite

Olav Revheim — Wed, 29 Feb 2012 10:31:15 +0000

The amphiboles in question can be seen here Richterite-Koksha and here Winchite-Koksha (Edit: Winchites changed to Richterites as per this thread)

I know this has been discussed before here, see link 1 to messageboard and link 2 to messageboard

The beautiful transparent amphiboles from the Koksha valley are labeled both as winchite and richterite at Mindat and also other webpages. It is absolutely possible that both of these amphiboles ( and multiple others as well for that matter) are present in these crystals. The "problem" is that I have not found any analysis supporting the winchite ID . There are no papers published on these crystals and the only two published analysis I have found is at rruff.info-richterite page, which gives richterite and fluororichterite respectively.

The first description of these crystals are from Dudley Blauwet (2004): "He later indicated that some fine single gem crystals of yellow potassian fluorian richterite, often associated with sodalite, were found at a place which was a day’s walk to the backside of the mountain housing the main lapis mine"- i.e near the Sar-e-Sang area. The association with sodalite (hackmanite) seems to be confirmed from photographed specimens at Mindat and other sites.

These crystals does not seem to be known by Shah Wali Faryad that publishes several papers on the petrology from the Sar-e-Sang area from 2002 and onwards. On the contrary he identifies (microprobe) several other amphiboles from the rocks associated with the lapis lazuli occurrences near Sar-e-Sang. These rocks originate from "primary carbonate and evaporite mixture that result (in) formation of variegated mineral assemblages. In addition, metasomatic reactions between granite/pegmatite band adjacent carbonate carbonate-evaporite" has formed various mineral assemblages.

Sodalite (which is assosiated w/ the richterite/winchite amphiboles) can only be found in what Faryad terms the 3rd stage metamorphosis in some calc-silicate rocks and mostly in the Na-Ca (K)-rich rocks that carry lazulite. These rocks have variable (Na+K)/Ca ratio as well as K/Na ratios. It is therefore quite likely that more than one amphibole is present in these transparent crystals. My questions on this matter are:

1- Min Rec 36:3 p294 is listed as the reference for winchite from Koksha. Can someone check this reference and see if the winchite ID is verified through analytical data?
2- The only analytical data I have found indicates that these amphiboles belongs in the richterite-series, but it is possible?/likely?/almost certain? that also other amphiboles are present in this association. How should these amphiboles be labeled ?
and
3- How should they be handled in a mindat context?

Any thoughts?

Olav

Re: Amphibole Group

Reiner Mielke — Sun, 26 Feb 2012 14:59:33 +0000

Got to love those new improved names: Sodic-ferri-ferropedrazite, Sodic-ferropedrazite and Sodic-ferripedrazite. LOL

Re: Amphibole Group

Olav Revheim — Sun, 26 Feb 2012 08:17:19 +0000

Thank you so much for your kind words, Mike. I respect those scientists that have chosen "the amphibole group" as their professional careers, and the effort they put into classifying a group of minerals that in all aspects resist classification.

That being said, the difficulty in identifying amphiboles (and tourmalines and micas and....) widens the gap between mineral collectors and amateurs like ourselves and science. That is, I think, worrying for a number of reasons.

Bart, I don't know if you have seen this: Amphibole group: programme for classifying microprobe or wet chemical analysis. I've found it helpful.

Today I found a simple error in the chemical formula for Ferropedrizite: The correct chemical formula should read LiLi₂(LiFe²⁺₂Fe³⁺Al)Si₈O₂₂(OH)₂, not NaLi₂etc.etc

Olav

Re: Amphibole Group

Bart Cannon — Sat, 25 Feb 2012 16:23:59 +0000

Mike,

The streak for all of the amphiboles I can think of would be more or less white.

Crushing an amphibole grain lightly in a mortar and pestle or even on a glass plate yields some color info that you wouldn't see via the streak test.

My list of amphibole crush colors is very cursory, and mostly presented in humor with a just tinge of exported, useful data.

I know that science marches on, and classification is an important part of learning about the minerals we all walk on.

But sometimes it becomes a little frustrating to stay in lock step with the shimmering changes underfoot.

Bart

Re: Amphibole Group

D Mike Reinke — Sat, 25 Feb 2012 15:48:57 +0000

Bart,
Even in a sour mood, you sum things up well. The comparison of car repair to mineral identifying is great. i can totally empathize since I recently threw away a ford (freestyle, don't go near them!!!) due to a $5600 tranny repair, if I'd have bothered.
Your list is new to me. By crush, do you mean the streak color, more or less? I want to keep a copy of that list of yours for much future reference!
I have wondered where nanotechnology would take minerals...It is scary. Too many names to learn, for one thing....

Olav,
If I could sum up your handling of these amphibole groups in one word, it would be "discreet". Don't know if I can give a higher commendation. You pepper your explanations w/ awareness of the difficulties and limitations of the science, w/o any grousing, (Hey, Bart! But even that is ok.) and for a newbie like me it is all very interesting. Early on, I found the 'black uglies' as someone called them, intriguing, and wanted to know more. So thanks.

Mike

Re: Amphibole Group

Linda Smith — Sat, 25 Feb 2012 07:11:22 +0000

Bart, wish there was "like" button on your post.

Re: Amphibole Group

Bart Cannon — Sat, 25 Feb 2012 04:14:30 +0000

Back when you could tune your car up with a timing light, a dwell meter and a screwdriver, mineralogy was simpler and more pleasant and useful.

Elongated silicates with a 56 degree cleavage angle were amphiboles, those with near 90 degree cleavage angles were pyroxenes.

The fussing was as follows:

White crushing amphibole = tremolite / actinolite.
Green crushing amphibole = hornblende / arfvedsonite
Blue crushing amphioble = riebeckite

Dark green pyroxenes = augite
Medium dark green pyroxenes = hedenbergite
Light green pyroxenes = diopside or omphacite

Now a high quality probe analysis is not enough to pigeonhole an amphibole. You need to know exactly what crystallographic "site" each element detected sits in. And their valence ! AND you need to know who is about to publish a revision before nailing an ID.

If we continue down this path, the trail to mineral identification will become pointless to the amateur, though a windfall to the rare species dealer. And is there enough funding to support the professionals as they split ever finer hairs ? Is there a practical value to the endeavor ?

I know this sentiment is old news. Please pardon my ill mood.

ClumperBart

Re: Amphibole Group

Ralph Bottrill — Fri, 24 Feb 2012 21:31:06 +0000

The Germans are so sensible Alfredo!

Re: Amphibole Group

Alfredo Petrov — Fri, 24 Feb 2012 19:08:33 +0000

Interesting, Everett. Years ago (15?) I wrote an article on asbestos mines in Bolivia for a german mineral magazine, and the editor took all the places I'd used the word "amphibole" and changed it to "hornblende". I questioned this editorial decision, but was overruled and it remained "Hornblende". I got the impression that hornblende was more or less synonymous with amphiboles among German collectors at least.

Re: Amphibole Group

Everett Harrington — Fri, 24 Feb 2012 17:53:23 +0000

Fun story, We were all at the Mineral Mansion talking about Amphibole minerals. We've decided that there is Tremolite and then the rest of the amphibole minerals.....hornblende :)-D:)-D :-D

cheers Michael Bainbridge!

E