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Ferro-winchite and the Bong Mine

Posted by D. Peck  
D. Peck June 24, 2016 02:15AM
The page for Ferro-winchite lists the Bong Mine, Bong, Liberia as a source locality. The page for the Bong Mine does not list Ferro-winchite, Should the mineral be listed with those found there?

Don Peck
Alfredo Petrov June 24, 2016 03:48AM
Don, technically, ferro-winchite is not listed (yet) on the Ferro-winchite species page for the Bong mine, Liberia, there are just a couple photos of it on the page, but you'll see it's not on the localities list lower down the page. The photographer listed the photos with that ID and so they went to that page, but there is no analysis or literature reference for the occurence of ferro-winchite there. As amphibole ID is a can of worms - (You might have both a powder XRD and a SEM/EDS analysis, the two most commonly available analyses, and still not know which amphibole species you have.) - and then there's the question re whether the ID was made before or after the IMA redefined amphibole species definitions and boundaries.... I leave this problem to our resident amphibole experts, like Olav, who may be able to dig up a confirming analysis... or not. :-S
Olav Revheim June 24, 2016 05:49AM
I did contact the uploader of this photo several years ago, and the specimens was procured from a mineralogist and they were supposedly analysed. I have not been able to confirm by which method or what the results were. I have not been able to find any literature references confirming the presence of ferro-winchite there, although the geology in the area can support the occurrence of winchite minerals.

I have kept it in as ferro-winchite on a "benefit of the doubt" basis so far, but as a header photo that is perhaps not sufficient.

On a more general basis, winchites are tricky minerals to identify even with microprobe as it is an intermediate composition between magnesio-hornblende and magnesio-arfvedsonite and their composition is generally close to either of these minerals or to richterite root name minerals. The intrinsic uncertainty in the Fe2/Fe3 calculations makes identification uncertain in most cases.

D. Peck June 24, 2016 05:55PM
Alfredo and Olav, Thank you for the explanation. And I understand the problem. Wish I had enough to have it analyzed, but I don't, only a single micro.

Don Peck
David Von Bargen June 24, 2016 10:55PM
There was a MS thesis that found magnesio-hornblende from there (Probe and Raman).
Peter Kohorst June 25, 2016 08:16AM
I have buyed a few years ago the ferro-winchite (xx) by German Dipl.-Min. Manfred Schaeffer from Detmold. As a companion pyrophyllite (xx) was specified. I'm basically assuming that crystal specimens were also analysed (XRS / EDS) before sale by reputable graduate mineralogists. The ferro-winchite occurs here black and (xx). The micaceous aggregates it might be the pyrophyllite (xx).

Why you did not asked me directly?
Olav Revheim June 25, 2016 12:57PM
Hi Peter,

I did contact you three or four years ago, you'll find the correspondance amongst your PM's. Your reply then was the same as now. The problem is that SEM-EDS and xrd is of little use in distinguishing Ferro-winchite from similar spesielt. I Hope this is an acceptable response from me, please let me know if you have further comments or questions

Peter Kohorst June 26, 2016 07:18AM
Hallo Olav,

yes, I understand, but I can't remember, what was 4 years ago and I delete my correspondence after some time, sorry. :-) But thank you for your response. Then, the next question is, what other analysing methods are senseful?
I think for example a microprobe (= Mikrosonde in German language) ? or others. What is the best method to analyse minerals from Amphibol-Supergroup or also from Pyroxen-Group?

Best regards

On a more general basis, winchites are tricky minerals to identify even with microprobe as it is an intermediate composition between magnesio-hornblende and magnesio-arfvedsonite and their composition is generally close to either of these minerals or to richterite root name minerals

Sorry, I have seen now your other answer.

Edited 4 time(s). Last edit at 06/26/2016 07:25AM by Peter Kohorst.
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