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Unusual bar pyrite from Nanisivik
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RussEpp




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PostPosted: Oct 29, 2020 12:20    Post subject: Unusual bar pyrite from Nanisivik  

This specimen has prominent rectangular-shaped pyrite crystals. What are the geological conditions that would cause this to occur? The main crystals are 9mm thick and up to 29mm long.


IMG_0296.JPEG
 Mineral: Pyrite
 Locality:
Nanisivik Mine, Nanisivik, Baffin Island, Nunavut Territory, Canada
 Dimensions: 84 mm x 45 mm x 38 mm
 Description:
 Viewed:  1078 Time(s)

IMG_0296.JPEG


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James Catmur
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PostPosted: Oct 29, 2020 13:23    Post subject: Re: Unusual bar pyrite from Nanisivik  

The conditions must favour growth in one plane. We see the same thing in some fluorite from the northern UK and pyrite from Spain.

I am not sure what the conditions are but maybe someone has thoughts on it

James
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James Catmur
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PostPosted: Oct 29, 2020 13:45    Post subject: Re: Unusual bar pyrite from Nanisivik  

A painting of a Spanish one


Pyrite.jpg
 Mineral: Pyrite
 Locality:
Valdeperillo, Cornago, Comarca Arnedo, La Rioja, Spain
 Dimensions: 12 cm x 12 cm x 10 cm
 Description:
 Viewed:  1011 Time(s)

Pyrite.jpg


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David K. Joyce




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PostPosted: Oct 29, 2020 14:26    Post subject: Re: Unusual bar pyrite from Nanisivik  

Hello Russ,
The pyrites are usually very bizarre and there are good reasons for it. It is not a simple concept. Thousands of unusual pyrites have come from the Nanisivik Mine.

The initial iron sulphide that crystallized in very good crystals was marcasite. Mostly, cyclic twins of marcasite. For some reason, almost ALL of the marcasite crystals were subsequently pseudomorphed to pyrite. If you look at the mindat location, you'll see many examples. Most interestingly, though, pyrite continued to crystallize ON the pseudomorphs as oriented overgrowths. The various initial blades of marcasite-turned pyrite have overgrowths oriented to the particular blade. This results in unusual aggregates of pyrite crystals. as very thin to very coarsely crystallized overgrowths. On the edge of the former pseudomorphs, these elongated overgrowths can look like bar growths of pyrite, in isolation.

Have a look at the Nanisivik Mine page of Mindat and you'll see many examples of elongated pyrite overgrowths.

Yours just formed very thick overgrowths and the original pseudomorph that supports the overgrowths is buried deep under the "bars". You can see it best, though in the aggregate on the right of your photo.

There was also a Mineralogical Record article on the subject; Vol: 21, Nov-Dec, 1990. There was also an article on the pyrite, specifically, by Dr. R I. Gait in the Min Record but I'm having a hard time finding it.

I hope this helps?!
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Bob Morgan




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PostPosted: Oct 29, 2020 14:54    Post subject: Re: Unusual bar pyrite from Nanisivik  

Bob Gait's article is in the July-August 1978 mineralogical Record. It explains well the faces of pyrite but doesn't get into overgrowths and the development of skewed crystal growth.

A lovely and interesting pyrite cluster.

Bob
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Linus




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PostPosted: Oct 29, 2020 15:05    Post subject: Re: Unusual bar pyrite from Nanisivik  

I recall that the Buick Mine in Missouri was very famous for rectangular pyrites, some up to 12 inchs long! The "Virtual Museum of Geology" website mentions that many of these had holes down the center suggesting that they originated as stalactic growths...
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RussEpp




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PostPosted: Oct 29, 2020 15:21    Post subject: Re: Unusual bar pyrite from Nanisivik  

Thanks David for the detailed reply and the references. I wasn't aware of the MinRec article and am fortunate to have that issue. The aggregate you were referring to on the right hand of the specimen is actually dark sphalerite crystals. I apologize for the picture, I am still learnig to take pictures of minerals. I examined the specimen very carefully including the sides and bottom and could see no sign of any pseudomorphing. I think this specimen looks more like the elongated pyrite crystals in figure 29 than the pyrite after marcasite in figure 31 in the Nanisivik article in the MinRec Vol: 21, Nov-Dec, 1990.
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lluis




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PostPosted: Oct 29, 2020 15:38    Post subject: Re: Unusual bar pyrite from Nanisivik  

Dear All

As Linus said, the ones from USA are widely known....
Myself have one and is a really long prism, making the ones from Nanisivik seen short...

Anyway, to me, just a nice curiosity...

With best wishes

LLuís
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David K. Joyce




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PostPosted: Oct 29, 2020 15:48    Post subject: Re: Unusual bar pyrite from Nanisivik  

I was referring to the furthest right pyrite on the right of the specimen. Figure 29, is, in fact, very thick overgrowths on a former pseudomorph. DKJ
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RussEpp




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PostPosted: Oct 29, 2020 15:57    Post subject: Re: Unusual bar pyrite from Nanisivik  

Thanks all for your responses. I have looked at a number of photos of pyrite bars from the Buick Mine, Missouri and they appear to be quite different. While some of them get quite long, they have a platy look, don't have striations and and least some of them have holes inside suggesting they are stalactic.
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RussEpp




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PostPosted: Oct 29, 2020 16:22    Post subject: Re: Unusual bar pyrite from Nanisivik  

David K. Joyce wrote:
I was referring to the furthest right pyrite on the right of the specimen. Figure 29, is, in fact, very thick overgrowths on a former pseudomorph. DKJ
.

Actually, According to the 1990 MinRec article, Figures 21,22,32,33, and 38 show pyritized marcasite overgrown by pyrite crystals while figure 29 is given as the "more familiar, striated cubes". I have looked carefully with the specimen in my hand and with a magnifiying glass and I still don't see any sign of original marcasite blades that may of pseudormorphed and been overgrown by pyrite..Maybe I just don't know what to look for.
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David K. Joyce




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PostPosted: Oct 29, 2020 16:43    Post subject: Re: Unusual bar pyrite from Nanisivik  

I'm sure you have noted that the pyrite crystals at Nanisivik are mostly combinations of various isometric forms which vary in dominance. in figure 29, the cube dominated but you will also see dodecahedral or pyritohedral forms beveling the sides and trapezohedral faces at each corner with a tiny octahedral face. These look more coherent to us because the cube dominates. In many of the other specimens, other isometric forms have more significantly sized faces and the pyrites become less recognizeable. The cubes with smaller additional isometric faces form oriented overgrowths on the original pseudomorphs, as well as any of the other forms when cubes are not dominant.
I doubt if you would ever see the marcasite remnants. They rarely, if ever exist. I've not seen them. The marcasite has been replaced by pyrite and then more pyrite has overgrown on the pseudos in oriented fashion. There should be no trace of the original marcasite blade. For instance in figures 32, 33 or 38, in the Min Record article. If you broke those specimens up, you would find no trace of the original crystals of marcasite. The only time you'll ever see them is if the overgrowths did not completely envelope the original pseudomorph.
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Linus




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PostPosted: Oct 29, 2020 16:46    Post subject: Re: Unusual bar pyrite from Nanisivik  

Actually there are some interesting thoughts on this at:
https://www.mineral-forum.com/message-board/viewtopic.php?t=2980 of this forum. Look down towards the bottom.
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Linus




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PostPosted: Oct 29, 2020 16:48    Post subject: Re: Unusual bar pyrite from Nanisivik  

i.e. bottom: Mar 23, 2013 by Pete Richards
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RussEpp




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PostPosted: Oct 29, 2020 17:00    Post subject: Re: Unusual bar pyrite from Nanisivik  

Thanks David , I understand much better now. I really like the Nanisivik pyrites for their complexity of forms and variety. By the way, I have collected many marcasite clusters from the Stony Mountain quarry just outside of Winnipeg. There are blades that look like spears and twinned crystals that look like Xmas trees. There are other forms as well. I don't know if they are pyrite pseudomorphs or not but they are certainly interesting. When I get better at photographing small items I will photograph some of them . A well-known collector was intrigued by the forms and talked about writing an article about them, but I don't think he ever did.
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PostPosted: Oct 29, 2020 17:01    Post subject: Re: Unusual bar pyrite from Nanisivik  

I'd look forward to seeing them! Thanks, DKJ
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PostPosted: Oct 29, 2020 17:52    Post subject: Re: Unusual bar pyrite from Nanisivik  

Your sample is definitely not pyrite over marcasite. I have several elongated specimens from there, one a bunch of simi aligned bars that compose a tube, another that is a pseudomorph of elongated marcasite blades, and the striations do not run the same way as in your sample.
Pete Richards et all wrote an article on such epitaxy and illustrates the differing pattern of crystal alignment and striations. See Pyrite and Marcasite Intergrowths from Northern Illinois, Mineralogical Record, 26, March-April 1995.
The only slight possibility of epitaxy might be suggested by photo 95G-8NW in Mindat, but even that doesn't resemble your sample.
Another photo does: R24-FUP. That one raises the mystery even higher. Surely there is some structural explanation for the consistent elongations. Perhaps overgrowths of pyrite whiskers?
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RussEpp




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PostPosted: Oct 29, 2020 18:33    Post subject: Re: Unusual bar pyrite from Nanisivik  

Bob Morgan wrote:
Your sample is definitely not pyrite over marcasite. I have several elongated specimens from there, one a bunch of simi aligned bars that compose a tube, another that is a pseudomorph of elongated marcasite blades, and the striations do not run the same way as in your sample.
Pete Richards et all wrote an article on such epitaxy and illustrates the differing pattern of crystal alignment and striations. See Pyrite and Marcasite Intergrowths from Northern Illinois, Mineralogical Record, 26, March-April 1995.
The only slight possibility of epitaxy might be suggested by photo 95G-8NW in Mindat, but even that doesn't resemble your sample.
Another photo does: R24-FUP. That one raises the mystery even higher. Surely there is some structural explanation for the consistent elongations. Perhaps overgrowths of pyrite whiskers?

Actually R24-FUP is the same specimen as the one in discussion.
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RussEpp




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PostPosted: Oct 29, 2020 19:21    Post subject: Re: Unusual bar pyrite from Nanisivik  

Hi Bob, Thanks for the reference. The 1995 article in the Min Rec by Pete Richards et al suggests that bars composed of single crystals are usually millimeter sized and the few larger bars that have been observed have a central cavity and are aggregates of several crystals or plates.
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Jordi Fabre
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PostPosted: Oct 30, 2020 05:04    Post subject: Re: Unusual bar pyrite from Nanisivik  

RussEpp wrote:
....The 1995 article in the MinRec by Pete Richards et al suggests...

In fact that article from the Min. Record is even downloaded here:
https://www.mineral-forum.com/message-board/viewtopic.php?p=19761#19761

I suggest to read the whole thread with the M.R. article, quiet interesting...
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