Passaic Pit, Sterling Hill, Ogdensburg, Franklin Mining District, Sussex Co., New Jersey, USA

I had XRD and EDS analyses done a few years ago on a sample of some of the dark brownish-black mica from the East Ore Vein of the pit to see if it is hendricksite. Dunn has little data in this area. The crystals are from marble in contact with or near the very tough, massive dark augite/mica/gahnite rock abundant in the pit. Attached are the analyses (Passaic Pit sample is labeled HTM-1), which were done by Fred Davis who volunteers at Yale Peabody mineralogy and has access to the equipment at University of New Haven, he's pretty experienced with the procedure and equipment. The XRD closest match is hendricksite (biotite standard is in there for comparison) and the EDS also suggested hendricksite. There is some Fe plus Mg and Mn, but this seems consistent with what I read in Dunn. This has not been published anywhere and I just uploaded a bunch of crystal photos to this page (more to come) so figured I get an opinion on these results and make changes if necessary.
Thanks
Harold Moritz

Maybe I'm out of the loop here, but it seems you did the analysis because Hendricksite is not on the species list for Sterling Hill, only Franklin?
Please forgive my ignorance. I have collected samples of Hendricksite from both localities. I have found whole crystals and crystal groups at Sterling Hill. Gary

"EDS also suggested hendricksite"

Not really - the Zn peak is too small and the Mg peak is too high (was the spectrum quantified?).

So which is it? Biotite or Hendricksite?

Gary,

The mineral IS on the species list for the Passaic Pit. Just sayin'. See ya tomorrow Fritz, and maybe you too, Gary.

Looks like hendricksite was added by Harold based on the specimens under discussion ...
Dunn does say that "At Sterling Hill, hendricksite is less abundant, due in part to a locally higher concentration of Mg and Fe in silicates, relative to Franklin. Frondel and Einaudi (1968) reported hendricksite occuring on one specimen with andradite, rhodonite, franklinite, and calcite, and on another with calcite and franklinite".
So hendricksite should be on the Sterling Hill list. Whether it is abundant in the Passaic Pit (specifically) - or even found there - is another question.



Edited 1 time(s). Last edit at 04/30/2011 12:14AM by Modris Baum.

As others have said, I think a lot of what has been collected in the pits at Sterling Hill is in fact Biotite and not true Hedricksite... the Zn content is too low. Seems that most of the "Hedricksite" I've collected in the Passaic and Noble Pits is from assemblages away from the orebody itself and in a matrix of fluorescent calcite with gahnite/pyroxene group minerals/etc... so Zn deficiency is not so surprisign when you consider the fairly sharp geochemical gradient in Zn and other metals away from the orebodies themselves [the Mn which causes the calcite to fluoresce is only necessary in very small quantities to do so.] I think there is a tendency to call all black Mica from Franklin and Sterling Hill "Hedricksite", obviously this is much rarer and more desirable than biotite or phlogopite. Anyways, just my two cents.

regards,
Philip

My 2 cents as well, these xtl don't even seem to have much visual similarity to typical hendricksite. Here is a specimen of an uncommon euhedrall xtl of hendricksite that I received from John Cianciulli many years ago.

MRH

Thanks for the comments. I did the analyses before I even knew about mindat, I wanted to know what species the mineral I've been collecting for 20 years is. I just got around to photographing/posting some of them. I dont know if the EDS spectrum was quantified, I'll ask Fred Davis who did it, to chime in on this discussion. The peaks on the XRD appear to match hendricksite better than biotite. Most of the description of the mineral in Dunn (1995) is regarding Franklin, which the photo posted by Mark Heintzelman appears consisted with (reddish-black). It should have been on the locality list according to Dunn (1995). The crystals do come from the Sterling Hill ore body, just a silicate rich - Zn poor section of the east vein left in place due to lack of ore. The occurrence of biotite, as described by Dunn (1995), is not within the ore body. The presence of Mg and Fe in the EDS is consistent with Dunn (1995). Whatever mineral it is it should be resolved as it is very abundant in the Passaic Pit and in large euhedral crystals - I have some that are over 7 cm across and 10 cm long.

I spoke with Pete regarding the possibility of hendricksite from the Passaic Pit on Saturday at the show.
He really had no opinion on the matter. As he states in his monograph "The extant knowledge is drawn entirely from Frondel and Ito (1966) and Frondel and Einaudi (1968); the paragenesis has not been investigated by the writer." Pete suggested that these articles should be consulted to see if they have specific information on occurences from the "Passaic Pit" (specifically) vs "Sterling Hill" (generically).
The articles are "Hendricksite, a new species of mica", Am Min 51, 1107-1123 and ""Zinc-rich micas from Franklin, New Jersey", Am Min 53, 1752-1754. I don't have access to these.

I don't think there is any debate about the presence of hendricksite at "Sterling Hill" or the need for it to be on that list. But if the "Passaic Pit" is to be treated as an distinct sub-locality then this needs independent verification.

BTW - Since "biotite" is now a series name, I'm confused by what the term "biotite standard" means.



Edited 1 time(s). Last edit at 05/02/2011 05:12AM by Modris Baum.

Links to the American Mineralogist papers:

[www.minsocam.org]
[www.minsocam.org]

Looks like there is quite a variation in composition and my one sample analysis is apparently not enough of a database to characterize the abundant mica in the whole Passaic Pit.

Looks like the second article (the one on Sterling Hill) provides no specific information on where in "Sterling Hill" the samples are from.



Edited 1 time(s). Last edit at 05/02/2011 02:39PM by Modris Baum.

The EDS was acquired from a polished, carbon-coated specimen, but the analysis was qualitative only, and the XRD is not a strong enough match to make a positive ID. In my opinion, there is currently not sufficient evidence in either EDS or XRD for a definitive call as hendricksite.

Hi Fritz,

Looking at the EDS pattern, your specimen looks like a ferroan phlogopite with a trace of zinc. The XRD has surprisingly broad peaks, but certainly looks like a mica. These data certainly don't agree well with the hendricksite end of the series, but as Uwe asked, "Were the peaks compared with a standard?" Even an unanalyzed Franklin hendricksite might be of help. The problem with EDS is that there is often the assumption that the peaks are "semi-quantitative", but the various elements are excited in different was depending on the operating volatages, condition of the counter, etc. Some labs do provide semi-quantitative EDS data, but it isn't known what the equipment used could deliver. Ordinarily, you would expect a higher peak for an element with larger atomic number and the zinc peak is probably disproportionately high relative to Mg. I am very glad to see that you used both XRD and EDS for your identification. One method gives you chemical information, one gives you structural information and you need to know BOTH to identify minerals with a high degree of certainty.

Best Wishes, Van King

Regarding the analyses, Fred Davis sent me the following:

I have reworked the XRD plot and reviewed the data based on what I've learned in the last 6 years. My response would be:

"The EDS was acquired from a polished specimen, but was qualitative only. "

The work was done on the SEM at AMNH, but no quantitative data was taken. Paul Bartholomew & I only had an afternoon to run a bunch of specimens, so the time spent was not sufficient for quantitative work. The AMNH operator had not set it up for semi-quant work, either, so we were stuck with qualitative data.

"The XRD is somewhat suggestive of hendricksite, but certainly not conclusive."

I replotted the XRD to make it a little more clear (what you have is my "old" method). The closest match for biotite uses "biotite-1M" data from MDI (the Materials Data Inc. database). The closest match for hendricksite comes from the same database. Given the difficulty in powdering a sheet silicate by hand, I would not be surprised by peak height and width issues.

The full range plot shows the right three peaks aligned better with hendricksite, and the middle of those for hendricksite alone is good position wise, but not so much for amplitude. The low d-spacing was crowded, so I expanded it in a second plot. Again, hendricksite has the edge, but is not definitive.

"There is not sufficient evidence in both EDS and XRD for a definitive call."

These are my thoughts today when revisiting the old data. It's just too close to call. Given the environment, I would lean toward hendricksite, but I wouldn't by the house on it. You are free to post any of my comments and the attached plot(s), or after your review we can discuss it further.

Fred

You must remember that the Passaic pit is a highly weathered zone within the southern basin of the Sterling ore body. The original Zn ore was weathered on surface down to about 600 feet. Zn was leached out and reprecipitated mostly as hemimorphite. The relic material was iron (and Mn)enriched as a result.

The first mining efforts here were for iron by mining the relic Fe-rich material in the center of the pit. This was later followed by the Zn mining of the hemimorphite. Thus, an Fe-rich, Zn-poor mineral suite is not unexpected.

I collected some of this black mica, in large crystals, a bit further north along the east vein. It certainly appears to be biotite but looks are deceiving. At Franklin much of the Hendricksite occurs in gangue within the ore body, often associated with Fe-garnet (andradite), and is a dark brown color. Of course, mica in the Franklin Marble, away from the ore bodies, is often Phlogopite.

Out of the 9 Sterling Hill analyses by Frondel and Einaudi (1968), they decided only 2 were hendricksite, and both those specimens were described as black, as were some of the Mn and Zn rich biotites. A few of the latter were described as bronzy black or dark reddish brown. So color doesnt help except to distinguish them both from phlogopite (pale yellow brown). I'd be happy to post these specimens as Mn and Zn rich "biotite", but which "biotite" species? Can we tell from the data available?

Black is a perfectly acceptable and normal color for iron-bearing phlogopite. The light colors in phlogopite tend to occur near the Mg-rich portions of the series.

Best Wishes, Van King

For what its worth, a dark green mica that I collected Feb '82 in the 600 level "gneiss zone", in the Sterling Mine, turned out to be Mn- and Zn- containing phlogopite, by qualitative EDS analysis. Was originally called 'biotite' by Bob Metzger

"All that is gold does not glitter; not all those that wander are lost," J. R. R. Tolkien

Proposed mineral additions to the Passaic Pit: malachite and bornite.

Azurite is already on the page, and I just finished doing some micro-photos (attached) of all three of these minerals from a single small specimen of marble found in the Passaic Pit last April. Much of this material has turned up in recent years, its occurrence in the unaltered marble wall just outside the "mud zone" is consistent with the statement on page 270 of Dunn (1995) (citing Metsger, 1990) "A halo of copper mineralization surrounds the mud zone at a distance of 15 feet." The quote does not differentiate whether that observation was within the pit or within the subsurface mined portion of the mud zone, but Dunn (1995) only describes the presence of these 3 minerals (see mineral descriptions pages 530, 618, 622) within subsurface levels at SH, not within the pit. However the abundance of this assemblage from recent Passaic Pit collection obviously extends the occurrence to the surface exposures. Chet, I'm going to post the azurite now and the other minerals when you are OK with it.
Fritz



Edited 1 time(s). Last edit at 11/27/2011 09:47PM by Harold Moritz (2).