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Pete Richards
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Joined: 29 Dec 2008
Posts: 841
Location: Northeast Ohio
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 Posted: Apr 20, 2020 16:20 Post subject: Another "where is it from" |
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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.
| Mineral: | Pyrite (epitactic on marcasite?) |
| Locality: | | [unknown locality] |  |
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| Dimensions: | Specimen is 3 cm across |
| Description: |
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| Viewed: |
11955 Time(s) |
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| Description: |
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| Viewed: |
11977 Time(s) |
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Collecting and studying crystals with interesting habits, twinning, and epitaxy |
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Bob Harman
Joined: 06 Nov 2015
Posts: 765
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| Posted: Apr 20, 2020 17:17 Post subject: Re: Another "where is it from" |
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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
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John Betts
Joined: 07 Jun 2012
Posts: 209
Location: New York City
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| Posted: Apr 20, 2020 17:43 Post subject: Re: Another "where is it from" |
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| 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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Joined: 29 Dec 2008
Posts: 841
Location: Northeast Ohio
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| Posted: Apr 20, 2020 17:59 Post subject: Re: Another "where is it from" |
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| 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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Kevin Conroy
Joined: 03 Dec 2018
Posts: 78
Location: Saint Louis, Missouri
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| Posted: Apr 20, 2020 18:28 Post subject: Re: Another "where is it from" |
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| 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
Joined: 07 Jun 2012
Posts: 209
Location: New York City
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| Posted: Apr 20, 2020 19:22 Post subject: Re: Another "where is it from" |
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| 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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Joined: 29 Dec 2008
Posts: 841
Location: Northeast Ohio
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| Posted: Apr 20, 2020 19:36 Post subject: Re: Another "where is it from" |
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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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Matt_Zukowski
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Joined: 10 Apr 2009
Posts: 736
Location: Alaska
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| Posted: Apr 21, 2020 00:24 Post subject: Re: Another "where is it from" |
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| 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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Joined: 07 Apr 2009
Posts: 4235
Location: Germany
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| Posted: Apr 21, 2020 01:40 Post subject: Re: Another "where is it from" |
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| 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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Pete Richards
Site Admin
Joined: 29 Dec 2008
Posts: 841
Location: Northeast Ohio
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| Posted: Apr 21, 2020 07:25 Post subject: Re: Another "where is it from" |
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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.
| Mineral: | Pyrite |
| Description: |
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| Viewed: |
11702 Time(s) |
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_________________
Collecting and studying crystals with interesting habits, twinning, and epitaxy |
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Bob Morgan
Joined: 18 Jan 2018
Posts: 249
Location: Savannah, Georgia
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| Posted: Apr 21, 2020 16:44 Post subject: Re: Another "where is it from" |
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| 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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