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Another "where is it from"
  
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Pete Richards
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PostPosted: Apr 20, 2020 16:20    Post subject: Another "where is it from"  

The specimen in question was accidentally included with a specimen I bought that clearly is from a different locality, so I don't know where this one is from.

This is a strange spiky group of distorted pyrite crystals; the basic unit is an asymmetric wedge-shaped crystal or sub-parallel crystal group. I identify this as pyrite based on what appear to be pyritohedral, cube, and octahedral faces in the right places relative to each other, even though the whole crystals are highly distorted.

There are a few small rather nondescript calcite crystals. The small chunk of matrix is a granular limestone, sugary in appearance, and is dotted with tiny chalcopyrite crystals. Even smaller, and scarce, are green blebs of an apparent copper secondary.

What makes the specimen particularly interesting is that the characteristic distortion of the pyrite crystals suggests that they are growing epitactically on marcasite needles.

If this material is common enough that someone recognizes it, I'd love to learn where it is from.



IMG_0086.jpg
 Mineral: Pyrite (epitactic on marcasite?)
 Locality:
[unknown locality]
 Dimensions: Specimen is 3 cm across
 Description:
 Viewed:  2992 Time(s)

IMG_0086.jpg



IMG_0095.jpg
 Description:
 Viewed:  2994 Time(s)

IMG_0095.jpg



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Bob Harman




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PostPosted: Apr 20, 2020 17:17    Post subject: Re: Another "where is it from"  

Just a guess, but with the limestone matrix and very small chalcopyrites, Pleasant Ridge Quarry and a couple of nearby quarries near Rensselaer Indiana produced somewhat similar examples of pyrite and marcasite associated with small nondescript calcites.
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John Betts




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PostPosted: Apr 20, 2020 17:43    Post subject: Re: Another "where is it from"  

Bob Harman wrote:
Just a guess, but with the limestone matrix and very small chalcopyrites, Pleasant Ridge Quarry and a couple of nearby quarries near Rensselaer Indiana produced somewhat similar examples of pyrite and marcasite associated with small nondescript calcites. BOB


The matrix is wrong for Indiana, which has gray-brownish limestone as the country rock.

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Pete Richards
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PostPosted: Apr 20, 2020 17:59    Post subject: Re: Another "where is it from"  

Bob Harman wrote:
Just a guess, but with the limestone matrix and very small chalcopyrites, Pleasant Ridge Quarry and a couple of nearby quarries near Rensselaer Indiana produced somewhat similar examples of pyrite and marcasite associated with small nondescript calcites. BOB


Thanks for your thoughts.

Actually, the Rensselaer calcites are highly distinctive, and these ain't them. And have you ever seen a sugary white limestone matrix - looking like a sugar cube - from Rensselaer? Brown sugar, maybe, but not white sugar. The Pleasant Ridge Quarry is where old blue jeans go to die and be preserved forever in bitumen!

Epitaxy between pyrite and marcasite was common there, but I never saw any that looked like this.

The calcites, however, are very interesting and the best are very fine!

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PostPosted: Apr 20, 2020 18:28    Post subject: Re: Another "where is it from"  

I think that this may be from one of the Viburnum Trend mines. The shape of the pyrite, and the size and color of the dolomite crystals, is very similar to some that I've seen from the mid to southern part of the Trend (either Brushy Creek, West Fork or Fletcher Mine) but not Sweetwater.
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John Betts




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PostPosted: Apr 20, 2020 19:22    Post subject: Re: Another "where is it from"  

Kevin Conroy wrote:
I think that this may be from one of the Viburnum Trend mines. The shape of the pyrite, and the size and color of the dolomite crystals, is very similar to some that I've seen from the mid to southern part of the Trend (either Brushy Creek, West Fork or Fletcher Mine) but not Sweetwater.


Once again, I would argue the matrix is wrong. Viburnum Trend country rock is gray-brown dolostone with small white dolomite crystals.

Years ago Vandall King taught me to look at the matrix when trying to determine an unknown locality. that rule has worked thousands of times. Don't look at the mineral. To me the matrix looks more like Germany, but the photos are not quite large enough to see well.

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Pete Richards
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PostPosted: Apr 20, 2020 19:36    Post subject: Re: Another "where is it from"  

Yeah, sorry, all I have to work with right now is my iPhone! The matrix IS really unusual - describing it as looking like a sugar cube is not far wrong. I think the green copper secondaries are unusual as well; wish I knew what they are.
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PostPosted: Apr 21, 2020 00:24    Post subject: Re: Another "where is it from"  

I would like to guess Nanisivik. Some of the matrix from there is pale i think, and the calcite and marcasite/pyrite look like they could come from there. I've never seen any copper secondaries but there is some Cu mineralization in the deposit, so who knows?
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Tobi




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PostPosted: Apr 21, 2020 01:40    Post subject: Re: Another "where is it from"  

John Betts wrote:
[...]To me the matrix looks more like Germany, but the photos are not quite large enough to see well.
John, which of the many many localities in Germany do you have in mind? "The matrix looks like Germany" is a hard guess for a country with hundreds of calcite + sulfides localities ;-) Maybe it is from Germany but I don't remember to have ever seen such a specimen, not from here or elsewhere, sorry :-(

Pete, is it confirmed that the main material on the specimen is without a doubt pyrite?
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PostPosted: Apr 21, 2020 07:25    Post subject: Re: Another "where is it from"  

Tobi wrote:
Tobi wrote:
...Pete, is it confirmed that the main material on the specimen is without a doubt pyrite?


It is not absolutely confirmed that this material is pyrite. I'm not even sure it is iron sulfide, and my access to means to test it is closed for now because of the pandemic.

However, as you know, the striations on a pyrite cube follow the three-fold symmetry of pyrite in their orientation, so that the ends of striations on any face are perpendicular to the striations on adjacent faces. This is true of the larger faces of these crystals as well - the slopes of the two sides of the "wedge" and the edges of the wedge. There are also minor faces which are about in the right position to be modifying faces of the pyritohedron, and others on the corners of the wedge that appear to belong to octahedra. In a few places there are crystals or parts of these wedges that have a more equant habit and look much more like pyrite cubes with pyritohedral and octahedral modifying faces.

That is my main evidence, other than color, for identifying it as pyrite....

I tried to make a drawing to suggest how these wedges are related to a normal pyrite crystal, only partly successful in my opinion. The back side of the wedge is parallel to the pyritohedral face outlined in red. Each wedge is actually a stack of several imperfectly aligned individual crystals.



SP.jpeg
 Mineral: Pyrite
 Description:
 Viewed:  2728 Time(s)

SP.jpeg



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Bob Morgan




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PostPosted: Apr 21, 2020 16:44    Post subject: Re: Another "where is it from"  

How about the Linwood Mine in Iowa? Ziga Minerals had several pyrite and marcasite epitaxy pieces at Tucson, and the related calcites are frosty white.
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