We use cookies to show content based on your preferences. If you continue to browse you accept their use and installation. More information. >

FMF - Friends of Minerals Forum, discussion and message board
The place to share your mineralogical experiences


Spanish message board






Newest topics and users posts
18 May-02:15:24 Re: the mim museum in beirut, lebanon (Tobi)
17 May-22:38:32 Re: collection of volkmar stingl (Volkmar Stingl)
17 May-03:14:23 Re: the mim museum in beirut, lebanon (Mim Museum)
16 May-08:20:07 Re: help with mineral identification in thin section from khibiny, kola peninsula (Daniel Garcia)
16 May-05:41:19 Re: help with mineral identification in thin section from khibiny, kola peninsula (Duncan Miller)
16 May-03:20:17 Re: help with mineral identification in thin section from khibiny, kola peninsula (Daniel Garcia)
16 May-01:49:42 Re: help with mineral identification in thin section from khibiny, kola peninsula (Duncan Miller)
15 May-22:21:35 Re: collection of volkmar stingl (Volkmar Stingl)
15 May-17:34:35 Gilbert gauthier - silvia's collection (Silvia)
15 May-09:05:40 Re: the mim museum in beirut, lebanon (Mim Museum)
15 May-06:13:55 Re: monthly mineral chronicles, mineral guides and more... (Crocoite)
15 May-02:23:13 The mizunaka collection - quartz (Am Mizunaka)
14 May-15:59:22 Re: help with mineral identification in thin section from khibiny, kola peninsula (Daniel Garcia)
14 May-12:47:43 Re: help with mineral identification in thin section from khibiny, kola peninsula (Pete Modreski)
14 May-12:03:14 Re: collection of volkmar stingl (Volkmar Stingl)
14 May-10:40:37 Help with mineral identification in thin section from khibiny, kola peninsula (Daniel Garcia)
14 May-10:25:53 Re: what is it? (Janjasina)
13 May-16:53:55 Re: silvia's collection (Silvia)
13 May-13:18:46 Re: elbaite, ending moor's head (Daniel Garcia)
13 May-10:19:46 Re: what is it? (Amir Akhavan)
13 May-10:18:08 Re: what is it? (Alfredo)
13 May-08:22:44 Re: collection of firmo espinar (Firmo Espinar)
13 May-08:22:07 Re: what is it? (Bob Morgan)
13 May-08:16:44 Re: what is it? (Firmo Espinar)
13 May-07:38:51 Re: what is it? (Fiebre Verde)

For lists of newest topics and postings click here


RSS RSS

View unanswered posts

Why and how to register

Index Index
 FAQFAQ RegisterRegister  Log inLog in
 {Forgotten your password?}Forgotten your password?  

Like
93405


The time now is May 18, 2022 08:59

Search for a textSearch for a text   

A general guide for using the Forum with some rules and tips
The information provided within this Forum about localities is only given to allow reference to them. Any visit to any of the localities requires you to obtain full permission and relevant information prior to your visit. FMF is strictly against any illicit activities related to collecting minerals.
Unusual habit for Pyrite.
  Goto page 1, 2  Next
  Index -> Minerals and Mineralogy
Like
20


View previous topic :: View next topic  
Author Message

Sante Celiberti




Joined: 04 Oct 2019
Posts: 683
Location: Tuscany


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Mar 18, 2022 16:38    Post subject: Unusual habit for Pyrite.  

Hello.

I recently acquired this South Tyrolean specimen attracted by the unusual habit of the Pyrite crystal. It currently is covered by a thin crust of Goethite, due to an incipient pseudomorphosis, but its nature is distinguishable.
All the exposed faces are surprisingly rhombohedral.
At first glance, I had mistaken it for a rhombododecahedral garnet, which also is present in the same locality.
Later I supposed a pseudomorphosis after Garnet, but the modifications on one corner suggest a primary Pyrite.
I've never seen this habit before. I suppose the rhombohedral faces are modifications of one of the main habits. But which?
What do the experts think?
Thank you in advance.

Best regards.
Sante



IMG_20220313_203725.jpg
 Mineral: Pyrite on Albite (variety pericline)
 Locality:
Val Pfunders (Val Fundres), Vintl (Vandoies), Val Pusteria District, Trento Province, Trentino-Alto Adige (Trentino-Südtirol), Italy
 Dimensions: 68 x 63 mm
 Description:
The Pyrite crystal size is 14 mm.
 Viewed:  1683 Time(s)

IMG_20220313_203725.jpg



IMG_20220313_203836.jpg
 Description:
 Viewed:  1684 Time(s)

IMG_20220313_203836.jpg



IMG_20220313_203228.jpg
 Description:
 Viewed:  1684 Time(s)

IMG_20220313_203228.jpg



IMG_20220313_210603.jpg
 Description:
 Viewed:  1683 Time(s)

IMG_20220313_210603.jpg



IMG_20220313_203003.jpg
 Description:
 Viewed:  1679 Time(s)

IMG_20220313_203003.jpg



IMG_20220313_202057.jpg
 Description:
 Viewed:  1683 Time(s)

IMG_20220313_202057.jpg



IMG_20220313_202939.jpg
 Description:
 Viewed:  1683 Time(s)

IMG_20220313_202939.jpg


Back to top
Reply to topic Reply with quote
Like
3
   

John Betts




Joined: 07 Jun 2012
Posts: 203
Location: New York City

View user's profile

Send private message

PostPosted: Mar 18, 2022 16:50    Post subject: Re: Unusual habit for Pyrite.  

Photos 4 and 5 look like a pyritohedron.
_________________
John Betts
Back to top
Reply to topic Reply with quote
Like
   

Sante Celiberti




Joined: 04 Oct 2019
Posts: 683
Location: Tuscany


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Mar 18, 2022 17:08    Post subject: Re: Unusual habit for Pyrite.  

Hi, John.

I agree on the 12 faces, but they look rhombohedral and not pentagonal.
This is my puzzle.

Greetings from Tuscany.
Sante
Back to top
Reply to topic Reply with quote
Like
   

Bob Carnein




Joined: 22 Aug 2013
Posts: 279
Location: Florissant, CO


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Mar 18, 2022 17:22    Post subject: Re: Unusual habit for Pyrite.  

Can you tell us how many of the big, striated faces there are (or would be, if the crystal isn't complete)? I have seen pyrite rhombic dodecahedra from Nanisivik, but the striations converge at the 3-fold axes.
Back to top
Reply to topic Reply with quote
Like
   

Sante Celiberti




Joined: 04 Oct 2019
Posts: 683
Location: Tuscany


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Mar 18, 2022 18:42    Post subject: Re: Unusual habit for Pyrite.  

Hi, Bob.

The exposed rhombohedral faces are 8.
For sure the crystal has 12.

Best regards.
Back to top
Reply to topic Reply with quote
Like
   

Pete Richards
Site Admin



Joined: 29 Dec 2008
Posts: 783
Location: Northeast Ohio


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Mar 18, 2022 18:44    Post subject: Re: Unusual habit for Pyrite.  

This is a very interesting crystal. Pyrite certainly can have rhombic dodecahedron faces, but this is uncommon and such faces are usually subordinate to other, larger faces. With the usual disclaimer about doing eyeball morphology from photographs, I think this could be as Sante interprets it - a crystal that is almost entirely a dodecahedron.

The main faces "bend" inward a bit at the three-way corner where an octahedral face would show up. If these little areas were sharp faces, they would belong to a trisoctahedron (red faces in the right diagram below).

Bob is right that striations on pyrite usually "converge at the three-fold axis". Usually, striations on pyrite result from oscillations between pyritohedral faces and/or the cube (yellow and brown faces in the left diagram). These striations are parallel to edges between the cube and adjacent pyritohedron faces, and in this case also their edges with the adjacent dodecahedron faces.

But the cube and pyritohedron are not present on this crystal, and the striations, less obvious and more widely spaced, can be seen as the beginnings of the bends that join at the three-fold axis. That is, these are oscillations between the dodecahedron faces and faces of an imperfectly formed trisoctahedron, or even the octahedron that is not present as actual, recognizable faces.

The crystal growth model would be that pyrite growth layers form on the dodahedral faces, and expand outward, but sometimes fail to meet at the three-fold axes, leaving rounded corners there.

This, of course, is conceptual. It could also be wrong!



pyrite.jpeg
 Description:
 Viewed:  1611 Time(s)

pyrite.jpeg



_________________
Collecting and studying crystals with interesting habits, twinning, and epitaxy
Back to top
Reply to topic Reply with quote
Like
3
   

Pete Richards
Site Admin



Joined: 29 Dec 2008
Posts: 783
Location: Northeast Ohio


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Mar 18, 2022 18:56    Post subject: Re: Unusual habit for Pyrite.  

John is right to compare the crystal's appearance with a pyritohedron - which also has 12 faces. The similarity can be seen if you mentally rotate my right drawing 90°, in which case the striations in each diagram are the same direction, and lead to the modifying faces which helped produce them. However, the corner of the crystal with the pyritohedron has two-fold symmetry, whereas the corner of Sante's crystal has three-fold symmetry.
_________________
Collecting and studying crystals with interesting habits, twinning, and epitaxy
Back to top
Reply to topic Reply with quote
Like
3
   

Sante Celiberti




Joined: 04 Oct 2019
Posts: 683
Location: Tuscany


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Mar 19, 2022 15:02    Post subject: Re: Unusual habit for Pyrite.  

Hello, Pete. I hope you are fine.

Thank you so much for your help that I was sure would come, but I'm still confused.
While I can see the dodecahedral habit in your drawings and understand the faces of the cube, pyritohedron and trisoctahedron, I still do not explain the origin of the twelve rhombic faces present in your drawings and in my crystal.
I would have expected a diagram showing how from a pentagonal-dodecahedron, possibly combined with other Pyrite habits, we arrive at a perfect (pseudo?) rhombic-dodecahedron.

My other problem seems to be of a semantic nature, nevertheless I believe that it concerns the rigor of crystallographic science.
For my professional training/deformation, which you know, I scrupulously adhere to a "definition". If this is important in all fields, it is all the more essential in the scientific field.
Now, the "definition" is obtained by "proximate genus" AND "specific difference".
As far as I know, the definition of pyritohedron is "A dodecahedron (proximate genus) WITH pentagonal faces (specific difference)".
The fact that it is typical of Pyrite does not exclude that it can be attributed to other crystals with a pentagonal-dodecahedral habit such as, for example, Carrollite.

Now, if you and John define my crystal as a pyritohedron I can only see two possibilities:
- or it is a deeply modified pyritohedron, I would say unrecognizable as I don't see any pentagonal face, and therefore I accept its definition, although I don't understand the nature of the modifications;
- or it cannot be defined as a pyritohedron, as it is a dodecahedron (proximate genus), but it does NOT have pentagonal faces (specific difference).
If we call pyritohedron a dodecahedron with rhombic faces, we would be allowed to call a garnet pyritohedron as well.

Most likely I'm wrong, but I don't know what.
Sorry if I bored you and thanks again for your precious time.

A warm greeting.
Sante
Back to top
Reply to topic Reply with quote
Like
1
   

Bob Morgan




Joined: 18 Jan 2018
Posts: 184
Location: Savannah, Georgia


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Mar 19, 2022 20:43    Post subject: Re: Unusual habit for Pyrite.  

I came up with the same conclusion as Pete - definitely dominant dodecahedral.
As to formation - the dodecahedron is a steeper angled face than the pyritohedron. The most common pentagonal being a (210) face Others are steeper (320) down through (760), and finally to the (110) dodecahedral.
I have seen dominant dodecahedral crystals - mostly only up to 5 mm. If striations were present they were oriented in the same zone as the cube and pyritohedrals that would be perpendicular to those on your crystal.
Striations that lie in that opposite direction are fairly common on pyritohedral faces. They are formed by diploid alternations with the pyritohedral form.
I've never seen them of the steeper dodecahedral faces, which as Pete points out would involve alternations between the dodecahedral surfaces and trisoctahedral surfaces. That's what makes your crystal such a mystery. Wondrous!
My guess is that trisoctahedral crystal faces developed and spread toward the threefold point in one direction and toward the dodecahedral in the other direction. As they accumulated in that direction they roughly aligned into the dodecahedral faces. This would be similar to highly striated and curved cube faces formed by pyritohedral layering roughly aligning in that form.
Back to top
Reply to topic Reply with quote
Like
   

Sante Celiberti




Joined: 04 Oct 2019
Posts: 683
Location: Tuscany


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Mar 20, 2022 15:53    Post subject: Re: Unusual habit for Pyrite.  

Hello, Bob. How are you?

Thanks for the intervention I've been waiting for.
I am pleased to note that, once again, your reading of a Pyrite crystal coincides with that of Pete.
I'm deeply sorry that I don't have sufficient crystallographic knowledge to allow me to fully understand the explanations of you two, although now I have fewer confusing ideas.
My little revenge :-) :-) :-) is that some aspects of this crystal are also a mystery to you and Pete.
I'm happy to have preferred this specimen to other more aesthetic pieces at last week's Bologna Fair.

Receive my best regards from Tuscany.
Sante
Back to top
Reply to topic Reply with quote
Like
   

Pete Richards
Site Admin



Joined: 29 Dec 2008
Posts: 783
Location: Northeast Ohio


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Mar 20, 2022 15:56    Post subject: Re: Unusual habit for Pyrite.  

Hi, Sante!

You ask excellent questions. Some do not have answers that are at once short and complete! And my reply is neither short nor complete.

The semantic questions first:

I agree that a pyritohedron is a dodecahedron with five sides (provided it is the only form on the crystal). It also must be a solid, all faces of which are equivalent to each other by the symmetry of the mineral, i.e. it is a single form, not a composite of two or more forms. The pentagonal dodecahedron with faces of the regular pentagon does not occur in minerals, so I guess it is not a pyritohedron. Yes, pyritohedra so defined can occur in other minerals with appropriate symmetry, such as sperrylite (in the same symmetry class as pyrite: 2/m -3) and cobaltite (with lower symmetry 23). Commonly used terminology is probably not as rigorous as you would like – the pyritohedron is named for the form in pyrite, but other pentagonal dodecahedra can exist (though rare) that probably most people would not identify as pyritohedra. Is the pyritohedron only one specific pentagonal dodacahedron, or is it a synonym for all pentagonal dodacahedra?

After all that, I did not mean to suggest your crystal was a pyritohedron, nor I think did John. The striations and slight bends at corners suggest the combination of a pyritohedron and a cube, but the similarity is misleading. Your crystal is a rhomb-dodecahedron (dodecahedron for short), not a pyritohedron. Nor is a garnet!

Now, to the crystallography: What follows is a discussion of geometry consistent with the symmetry class of pyrite. It is not meant to suggest that all of the details describe actual pyrite crystals, only ones that are geometrically consistent with pyrite. Crystal growth constraints guarantee that the set of actual pyrite crystals is far more limited.

Pyrite has three axes at right angles, consistent with axes for a cube, though these axes in pyrite are only of two-fold symmetry, not four, as shown by the common striations on cube-shaped crystals. Pyrite also has four three-fold axes that emerge from the corners of the cube, and additional symmetry elements. A plane in the space defined by these (two-fold) axes can intersect all three of them, two of them, or only one of them. This plane is not alone – the symmetry requires that there are other planes which are equivalent by rotation (or other symmetry operations, which I’m leaving out for now). This family of planes, all at the same distance from the origin to preserve the symmety, intersect each other, and the minimum volume that they enclose is the solid, the “crystal”, a product of the symmetry and the orientation of the “generating” plane.

Given the symmetry of pyrite, a randomly oriented plane, which intersects all three axes and at different distances from the origin, “forms” a diploid, the general form for pyrite’s class, which has 24 faces. Almost any randomly chosen plane would form a diploid.

But there are special situations – which because of crystal growth principles typify most crystal faces. These occur when the plane is parallel to one or two of the axes – it never crosses them, and/or when the plane intersects two or more axes but at the same distance. In these positions, some of the planes may coincide (when the plane is parallel to one or two axes), so the number of faces is reduced to 12 or 8 or 6. Or their positions may add "extra" symmetry to the resulting solid, compared to that of the symmetry class as a whole. A pyrite cube, as a geometric object, has four-fold symmetry, for example, even though the symmetry of the mineral does not really include a four-fold rotation, as striations or extra faces may reveal.

The two diagrams below show a kind of triangular graph of pyrite crystallography. The left corner of the triangle is the position of the cube, the special case where each face is parallel to two of the main axes; its Miller indices are {100}, reflecting the fact that its faces each only intersect one axis, and representing, as part of the form, the faces (010), (001), (-100), (0-10), and (00-1) in addition to (100). The right corner represents the rhomb-dodecahedron, {110}, each of whose faces intersect two of the axes at equal distances from the origin but are parallel to the third. The top corner represents the octahedron {111}, whose faces intersect all three axes, but at the same distance from each axis. These three forms are fixed forms – there is only one cube, only one octahedron, and only one rhomb-dodecahedron.

Along the horizontal line at the bottom, there are forms that intersect two axes, but at different distances from the origin. Given the mathematics of Miller indices, forms along this and the other two lines can be computed as sums of the end-members – either equally or unequally weighted. Examples are {210}, the typical pyritohderon of pyrite, as well as {310}=2{100}+{110}, {340}, {910}, and any {hk0}, where h and k are any integers that are not the same. These are all consistent with pyrite symmetry, though most are destined to be rare or unknown in the real world of pyrite crystal growth.

Along the left diagonal line, between the cube and the octahedron, lie the trapezohedra, which intersect all three axes, two at the same distance and the third at a smaller distance, with indices {hkk}, where h is greater than k. Along the right diagonal line lie the trisoctahedra, with indices {khh}, where h is greater than k.

The pyritohedron, trapezohedron, and trisoctahedron are variable forms, but their variability is constrained by the relationships just described. They have to “stay on their lines”.

Any place in the middle of the triangle is corresponds to a diploid. Diploids have Miller indices {hkl}, where h, k, and l are any three different integers, representing intersects at different distances on the three axes. The diploid is variable, only constrained in the sense that if two or more of its intercepts are the same, or one or more is parallel to an axis, it is no longer a diploid but one of the special forms, possibly with fewer faces.

As the second diagram shows, forms that are closer to one of the endpoints look more like the endpoints. The angles between their faces and the faces of the endpoint are smaller than with the other endpoint. Because Miller indices are reciprocals of intercepts, the indices of the variable form are “nearer” to those of the end form. In this sense, for pentagonal dodecahedra, {210} is in the middle, {410} is closer to the cube, {10 1 0} (or equivalently but non-conventionally {1 0.1 0} ) would be even closer, but {540} would be closer to the dodecahedron.

All this prompted by Sante’s question about the relationship between the pyritohedron and the dodecahedron! In one sense, the dodecahedron is one limiting form for the pyritohedron, the other being the cube. The dodecahedron is also a limiting form for the trisoctahedron and even the diploid.

I hope all of this makes some sense. This fluid but constrained relationship between different forms is, to me, one of the delightful aspects of the crystallography of minerals.



Pyrite xllography 6.jpg
 Description:
 Viewed:  1290 Time(s)

Pyrite xllography 6.jpg



Pyrite xllography 13.jpg
 Description:
 Viewed:  1292 Time(s)

Pyrite xllography 13.jpg



_________________
Collecting and studying crystals with interesting habits, twinning, and epitaxy
Back to top
Reply to topic Reply with quote
Like
3
   

Pete Richards
Site Admin



Joined: 29 Dec 2008
Posts: 783
Location: Northeast Ohio


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Mar 20, 2022 16:07    Post subject: Re: Unusual habit for Pyrite.  

I forgot to comment that carrolite cannot have a pyritohedron. Its crystal class is 4/m -3 2/m, and in that symmetry class the form in that position would be a tetrahexahedron, not a pyritohedron.
_________________
Collecting and studying crystals with interesting habits, twinning, and epitaxy
Back to top
Reply to topic Reply with quote
Like
   

Sante Celiberti




Joined: 04 Oct 2019
Posts: 683
Location: Tuscany


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Mar 20, 2022 17:35    Post subject: Re: Unusual habit for Pyrite.  

Hello, Pete.

Believe me, I'm so mortified for taking all this time from you!
I am consoled by the fact that this stupendous Lectio magistralis will be useful not only to me, who at the moment only understand a part of it, but to all those who are approaching crystallography. The diagrams you attached were also of great help.
At the end of your reading I realize that the more I try to go into mineralogy, the more I recognize my ignorance.
But I'm on this Forum to learn, if it's still possible at my age.
Meanwhile, I enjoy my nice rhomb-dodecahedron. :-)

I really thank you very much.
All the best.
Sante
Back to top
Reply to topic Reply with quote
Like
1
   

Sante Celiberti




Joined: 04 Oct 2019
Posts: 683
Location: Tuscany


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Mar 20, 2022 17:45    Post subject: Re: Unusual habit for Pyrite.  

Pete Richards wrote:
I forgot to comment that carrolite cannot have a pyritohedron. Its crystal class is 4/m -3 2/m, and in that symmetry class the form in that position would be a tetrahexahedron, not a pyritohedron.


You are right, Pete.
Believe it or not, I had in mind my Cobaltite and I wrote Carrollite.
This can happen when we approach eighty...
Back to top
Reply to topic Reply with quote
Like
   

Bob Morgan




Joined: 18 Jan 2018
Posts: 184
Location: Savannah, Georgia


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Mar 22, 2022 16:01    Post subject: Re: Unusual habit for Pyrite.  

Are you sure this is pyrite, because magnetite often takes a dominant dodecahedral form with striations running in that direction?.
Back to top
Reply to topic Reply with quote
Like
2
   

Sante Celiberti




Joined: 04 Oct 2019
Posts: 683
Location: Tuscany


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Mar 22, 2022 17:09    Post subject: Re: Unusual habit for Pyrite.  

Hi, Bob. Thanks again for your interest.

Since Trentino-South Tyrol is quite rich in Magnetite, I don't exclude that it can be found also in Pfunders Valley, although Mindat doesn't mention it in this locality.
However, consider that the Magnetite of this region always shows the sharp octahedral habit so typical of the Alps.
Furthermore, under the Goethite crust, color and luster are unmistakably those of Pyrite.
Just to be sure, I tried the magnet test but the result, as I assumed, was negative.
I fear this crystal will continue to be a puzzle.

Warm greetings.
Sante



IMG_20220322_220826.jpg
 Description:
 Viewed:  1079 Time(s)

IMG_20220322_220826.jpg


Back to top
Reply to topic Reply with quote
Like
1
   

Bob Morgan




Joined: 18 Jan 2018
Posts: 184
Location: Savannah, Georgia


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Mar 22, 2022 17:48    Post subject: Re: Unusual habit for Pyrite.  

Not magnetite - how about chalcopyrite? I have one from Bulgaria that has the same dodecahedral shape with similar striations and brown flaky coating.
The growth development seems to be octahedral layers with edges that stacked and roughly aligned into the striated dodecahedral faces.

I'm looking away from pyrite because the striations aren't right, and the mystery must have a more satisfying resolution.
Back to top
Reply to topic Reply with quote
Like
1
   

Roger Warin




Joined: 23 Jan 2013
Posts: 1019


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Mar 23, 2022 09:13    Post subject: Re: Unusual habit for Pyrite.  

Hello,
Can we consider the measurement of angles between edges as long as the face is perpendicular to the axis of the lens?
Back to top
Reply to topic Reply with quote
Like
   

Sante Celiberti




Joined: 04 Oct 2019
Posts: 683
Location: Tuscany


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Mar 23, 2022 15:41    Post subject: Re: Unusual habit for Pyrite.  

Roger Warin wrote:
Hello,
Can we consider the measurement of angles between edges as long as the face is perpendicular to the axis of the lens?


I can't answer for sure, but I would say by feeling that if a face of a crystal is perpendicular (in both directions) to the axis of the lenses it is like having -in the purpose of measuring angles- the crystal itself in your hands.
Back to top
Reply to topic Reply with quote
Like
   

Sante Celiberti




Joined: 04 Oct 2019
Posts: 683
Location: Tuscany


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Mar 23, 2022 16:27    Post subject: Re: Unusual habit for Pyrite.  

Bob Morgan wrote:
Not magnetite - how about chalcopyrite? I have one from Bulgaria that has the same dodecahedral shape with similar striations and brown flaky coating.
The growth development seems to be octahedral layers with edges that stacked and roughly aligned into the striated dodecahedral faces.

I'm looking away from pyrite because the striations aren't right, and the mystery must have a more satisfying resolution.


Hello, Bob.

Your tenacity reveals a true investigative attitude. :-)
Chalcopyrite, not mentioned by Mindat in Pfunders Valley, is still present in Trentino-South Tyrol, albeit generally in millimeter crystals, even more than Pyrite.
It was not easy to carry out the only mechanical test possible (hardness) without seriously compromising the only crystal present on my specimen.
With a steel sewing needle (estimated hardness 4-4,5) I first carried out the test on a sample of Romanian Chalcopyrite obtaining a positive result (the small groove left by the needle is visible).
After that, I had to identify in my sample a hidden area where I could carry out the test without this being noticed in a normal exposure of the specimen.
Also in this case the result was positive, although the groove left by the needle is not easily framed by the lens.
Therefore it would seem that my crystal, purchased as Pyrite, is instead Chalcopyrite.
Now it is a question of interpreting its shape.
And, yes, it looks like Bulgarian Chalcopyrite loves rhombic faces.

Thank you, Bob.
Sante



IMG_20220323_183615.jpg
 Mineral: Chalcopyrite
 Description:
Romanian Chalcopyrite before the hardness test.
 Viewed:  917 Time(s)

IMG_20220323_183615.jpg



IMG_20220323_183732.jpg
 Mineral: Chalcopyrite
 Locality:
Romania
 Description:
Same crystal (in the middle) after the hardness test.
 Viewed:  919 Time(s)

IMG_20220323_183732.jpg



IMG_20220323_134016.jpg
 Description:
Identified area on my crystal for the hardness test.
 Viewed:  917 Time(s)

IMG_20220323_134016.jpg



IMG_20220323_184813.jpg
 Description:
The groove left by the steel needle.
 Viewed:  917 Time(s)

IMG_20220323_184813.jpg



IMG_20220323_211452.jpg
 Mineral: Chalcopyrite
 Locality:
September Mine (9th of September Mine) , Madan mining area, Rhodope Mountains, Smolyan Oblast, Bulgaria
 Description:
Rhombic faces in a Bulgarian Chalcopyrite.
 Viewed:  918 Time(s)

IMG_20220323_211452.jpg


Back to top
Reply to topic Reply with quote
Like
   
Display posts from previous:   
   Index -> Minerals and Mineralogy   All times are GMT - 5 Hours
Page 1 of 2
  Goto page 1, 2  Next  

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum


All pictures, text, design © Forum FMF 2006-2022


Powered by FMF