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Amphibole Group
February 22, 2012 07:40PM
    
I have volunteered to write "best mineral" articles on the various minerals in this group. I have approached these minerals with a great deal of respect and humility as I am a true novice on the matter

As a consequence, I try my very best to find all the information I can as for each amphibole mineral before I put it down in writing. Every now and then I find mismatches between various literature and Mindat. I have posted a few messages in the "mistakes and error" forum on some of these mismatches, but I have come to learn that it hard to be sufficiently confident to claim any given mismatch as an "error" or a "mistake". For the amphiboles, I have learned, there are many shades of gray between "correct" and "error".

In addition there are many things I just don't know, issues I would like a second opinion on or just want to discuss, and I am pretty sure that I am not the only one that has an amphibole related question.

I hope that this talk page topic can become a place for discussion on this particular group of minerals.

Olav
avatar Re: Amphibole Group
February 23, 2012 10:48AM
    
Amongst the general problems you will find in dealing with amphiboles is that a full chemical analysis is required to give a specimen a precisely correct name (including for example distinction of Fe2+ from Fe3+ ), and also that their classification and nomenclature has been radically changed (at least once) from what it was at one time.

So finding "literature/Mindat mismatches", or amphibole specimens whose label shows a name not found in a modern database, or a different name on an old label from that on a more recent one (perhaps because the specimen has been re-classified in light of a new analysis, or simply because the original name has been changed), are unfortunately going to be common problems when trying to find your way through the maze of amphibole nomenclature.

Good luck!

Pete N.
Re: Amphibole Group
February 24, 2012 09:08AM
    
Thanks Pete,

I know this is a very complex group, both because of it's complex and flexible chemistry, the difficulty in identifying these minerals and also because of the changes in the nomenclature. Just to get started, I would like to address the following:

Ferripedrizite was originally described in 2002 ( Cabellaro et.al.) from Arroyo de la Yedra. A year later, the nomenclature was changed, so that Cabellaro's ferripedrizite became sodic-ferripedrizite ( Leake et.al.(2003): NOMENCLATURE OF AMPHIBOLES: ADDITIONS AND REVISIONS TO THE INTERNATIONAL MINERALOGICAL ASSOCIATION’S 1997 RECOMMENDATIONS), and the mineral ferripedrizite was consequently discredited.

The detailed mineral description for Arroyo de la Pedra, has the status of this mineral to "believed valid". I'd like to add a comment to this entry stating:

"Due to nomenclature changes in the amphibole group, the mineral originally described as ferripedrizite has been reclassified as sodic-ferripedrizite, still maintaining the original chemical formula. Ferripedrizite is consequently discredited"

and also add the same description to the ferripedrizite mineral page.

I know this is an obscure mineral without much relevance for most people, but I still think this is something that should be changed. Any comments?

Olav
avatar Re: Amphibole Group
February 24, 2012 10:44AM
    
I agree that Mindat should use the latest IMA approved nomenclature, so as ferripedrizite has been discredited/renamed, I would suggest that to avoid confusion and duplication of data, although the fact that it has been discredited is mentioned on its Mindat page (ferripedrizite), the detailed description of its properties should be removed from that page, leaving only a brief reference to the name as a synonym of sodic-ferripedrizite, with the new name sodic-ferripedrizite as a hyperlink to the full description, optical data etc for the species, similarly to what has been done for other discredited/synonym names such as Sphene, a synonym of the currently accepted name "Titanite". (although personally I prefer sphene as the name of that mineral!)

Pete N.
Re: Amphibole Group
February 24, 2012 01:15PM
Olav, I suggest using the word "renamed" instead of "discredited", as there wasn't anything wrong with the original description.
Re: Amphibole Group
February 24, 2012 02:26PM
    
Alfredo, I've updated the locality, but I don't seem to be able to change the mineral page.

Olav
Re: Amphibole Group
February 24, 2012 02:28PM
    
Seems like another unnecessary IMA name change. What was wrong with the name ferripedrizite? They were happy with leakeite, why didn't they change that to sodic-leakeite to go with sodic-ferripedrizite?
avatar Re: Amphibole Group
February 24, 2012 02:37PM
If they don't change the Amphibole group names every five years the people in the group will have to find productive work to do :)

Jolyon
avatar Re: Amphibole Group
February 24, 2012 05:53PM
    
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 smileys with beersmileys with beer grinning smiley

cheers Michael Bainbridge!

E
Re: Amphibole Group
February 24, 2012 07:08PM
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.
avatar Re: Amphibole Group
February 24, 2012 09:31PM
The Germans are so sensible Alfredo!

Regards,
Ralph
Re: Amphibole Group
February 25, 2012 04:14AM
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
avatar Re: Amphibole Group
February 25, 2012 07:11AM
    
Bart, wish there was "like" button on your post.

Linda Smith
Rock Mama and Boogie Boarding Grandma
Re: Amphibole Group
February 25, 2012 03:48PM
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
February 25, 2012 04:23PM
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
February 26, 2012 08:17AM
    
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
February 26, 2012 02:59PM
    
Got to love those new improved names: Sodic-ferri-ferropedrazite, Sodic-ferropedrazite and Sodic-ferripedrazite. LOL
Re: Amphibole Group-Afghani winchite vs. richterite
February 29, 2012 10:31AM
    
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



Edited 2 time(s). Last edit at 03/24/2012 08:19PM by Rob Woodside.
Holmquistite- Koktokay China
March 06, 2012 12:16PM
    
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
avatar Re: Holmquistite- Koktokay China
March 06, 2012 12:46PM
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
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