FMF - Friends of Minerals Forum, discussion and message board

[John S. White]

I have been very busy since Knut posted his query ( https://www.mineral-forum.com/message-board/viewtopic.php?p=4021#4021 ) on March 16 about the Smithsonian's green "herderite" from Pakistan whose label implies that it is fluorine-rich:

"One of the new specimens in the exhibit has been labeled "Herderite" from Gilgit in Pakistan. Also the accompanying chemical formula indicates the mineral to be F-dominant rather than the much more common Hydroxyl-Herderite. As far as I know there has been no published data to support the occurence of Herderite (F-dominant) from this area and I would have loved to know if this Herderite-group mineral really has been analyzed to prove the correct ID. Maybe if John S. White sees this post he still has contacts at the Smithsonian that could clarify the issue. Especially in such a prominent museum you would expect labels with chemical formulas to give the correct specimen ID."

I have had to educate myself on the herderites. The first thing I learned is that the 2008 edition of Fleischer's Glossary of Mineral Species describes herderite as a "doubtful species." This is because, apparently at the time of publication, the author of the Glossary did not believe that the gem from Brazil which was shown to be herderite by optics alone was sufficient to establish the legitimacy of herderite. Curiously, at the same time the Glossary was published, a paper by George Harlow and Frank Hawthorne appeared in the American Mineralogist documenting herderites by chemical analysis from Myanmar and from China, and also stating that herderite from Namibia is likely. So far, no evidence has been obtained that fluorine-dominant herderite has been found in Pakistan. Additionally, Luiz Menezes has reported that all of the herderites from Brazil that he has analysed are hydroxylherderite. More to come on this subject, I hope.

[Aymeric]

As far as I know, most (if not all ?) pakistan herderite is actually herderite-hydroxyl-herderite as analysed crystals have shown to be mid-range between the F and OH herderite. There was an article about it on gia website, but it's gone for some reason.

[keldjarn]

John,
Thanks for taking the time to respons. In the meantime Gail Spann has posted a reply from the Smithsonian stating that they have not analyzed the specimen - only made the label based on the dealer`s label. I am aware of the Am.Min article and also other published data documenting the existence of true F-dominant Herderites, but I believe so far all the analysis performed on Herderite-group minerals from Pakistan and Afghanistan have shown them to be on the Hydroxyl-Herderite side of the 50/50 divide. I think until published data emerge one should be very careful labeling specimens as "Herderites" with chemical formulas to indicate F-dominance. It seems that Hydroxylherderites are the by far most common member of this group.
Knut

[Joan Massagué]

John, Aymeric,

Thank you for this information. I'm not sure if this will clarify of complicate things, but here I go:

There are several sources of (hydroxyl)herderite in Pakistan. The two most prominent seem to be the Sassi/Dassu area at the footsteps of Mt Haramosh, in the Gilgit division, and the Chhappu/Dassu area in the Braldu valley, up from the Shigar valley, in the Baltistan division. Both sources are mentioned in the "Pakistan" issue of extraLapis English. In their seminal article (Min. Rec. 16:393-411, 1985), tby Kazmi, Peters and Obodda refer to "Dusso, Gilgit division" as the source of apple green crystals at the time. The authors write that analysis of one such specimen preserved in the AMNH collection falls near the mid-point between herderite and hydroxylherderite, or CaBe(PO4)(OH,F), as one of you says. Herb Obodda was the source of my specimen below, which was supplied as herderite/hydroxylherderite, from Dassu, Gilgit division. So, circumstantially at least, all seems to support the notion that the material from Sassi/Dassu/Haramosh is herderite/hydroxylherderite. The question is whether the material from Chhappu is also herderite/hydroxylherderite or, as John quotes from Menezes, just plain hydroxylherderite. Does any of you know?

[keldjarn]

A metaanalysis of all published analytical data for minerals in the Herderite-Hydroxylherderite seies would clearly show that nearly all reliable analysis fall in the Hydroxylherderite part of the 50/50 divide. But there are also sound evidence that the F-dominant Herderite actually exist in nature as previously cited references show. Considering the uncertainties inherent in the F/OH-analysis I interpret also the statement that "a specimen in the AMNH collection is close to the Hydroxylherderite-Herderite divide" as saying that so far all analysis of Hederite-group minerals from Pakistan and Afghanistan show them to be Hydroxylherderites. From a scientific point of view either all minerals in the series should be labeled "Herderite-group" or "Herderite-Hydroxylherderite series", or only specimens from the few localities where the F-dominant Herderites have been clearly demonstrated should be given the name "Herderite" and all other specimens could safely be labeled "Hydroxylherderite".
Knut

[Jordi Fabre]

In September 2007 several Herderites appeared in Pakistan in a small village named for the vendor: Sassi, in Haramosh Mountains, Gilgit, Pakistan.
I ordered analysis of one of these Herderites and the analysis don't showed Fluor. I would like publish this analysis here but for the moment I can't find it.

Hopefully it helps.

Jordi

[John S. White]

It is indeed unfortunate that so many of the samples of herderite/hydroxylherderite appear to have compositions near the middle of the series, making it difficult to assign a reasonable name collectively to all from just one particular locality. I really do not like having to call them herderite/hydroxylherdite. It would be so much better if the end members were herderite-(F) and herderite-(OH), then we can use the name herderite when we do not know where in the series a sample falls. Let us hope, and perhaps urge them to do so, the IMA makes this change.

[alfredo]

In my opinion, when an -F or -OH analogue of a species is discovered, the "renaming" of the other member should be automatic and self-evident, for clarity; it should not require an IMA ruling. I already use "herderite-F", in order to promote clarity; then no confusion is possible. Science is all about transmission of information with clarity and, in this case, "anarchic" behaviour (ie. not waiting a decade for an IMA decision) promotes clarity rather than detracts from it.

[Joan Massagué]

Alfredo: amen.

Joan

[keldjarn]

I fully agree with John and Alfredo concerning the naming of Herderite-group minerals. We would probably not have had this problem IF the original analysis were correct when Herderite was named as I understand the material from the type locality is really Hydroxylherderite ! Then the "common" group member would have been "Herderite" and the more unusual "Fluorherderite". Thus works well with i.e. Vesuvianite. Anyway, renaming the minerals Herderite-F and Herderite-OH makes more sense than i.e. changing an established mineral name like "Hancockite" to "Epidot-Pb" - but that is another discussion.

Knut

[Peter]

The pegmatites carrying "Herderite" on the west side of Haramosh Peak, Haramosh Mountains are located on the south side high above Sassi village and some are on the backside of the ridge (slope leading down to Dusso village to the west) thus called Dusso. You are lucky to have correctly labeled specimens from these interesting pegmatites. They are located at high altitude 4000m+ and up.

[John S. White]

I tend to agree with Alfredo and believe he has the right response, the IMA be damned. Perhaps it is time that the mineral community made an effort to influence the IMA's often
ill-considered decisions. Lets adopt herderite-(F) and use herderite for the series.