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marco campos-venuti
Joined: 09 Apr 2014
Posts: 207
Location: Sevilla
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Posted: Jun 11, 2014 06:32 Post subject: Re: 2014 - International year of crystallography: for example, pyrite. |
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Why not pyrite pseudo after pyrite?
Normal case of pyrite growing above pyrite is that the crystal continues to grow and nothing chance.
When we have epitaxial growths it is because for some reason, the nucleation increases and many small crystals grow oriented above the face of the previous pyrite, as is the case of these pictures (Las Palmas, Peru).
What is the reason for the disorder in the Racracancha crystals? Maybe the original crystal was in an unstable chemical condition and starts to be replaced by, for example, limonite. Before the process was completed, chemical conditions come back and pyrite is stable again, and starts to regrow replacing limonite. Result: pyrite pseudo after pyrite. (or pyrite pseudo after unknown mineral pseudo after pyrite). A little tricky, but realistic.
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Two generation of pyrite with epitaxial growths Las Palmas, Perú 12 cm |
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Rei
Joined: 09 Apr 2014
Posts: 228
Location: Höfuðborgarsvæði
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Posted: Jun 11, 2014 06:53 Post subject: Re: 2014 - International year of crystallography: for example, pyrite. |
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Wow, that's... unusual.
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prcantos
Site Admin
Joined: 17 Apr 2012
Posts: 243
Location: Granada (Spain)
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Posted: Sep 29, 2014 04:39 Post subject: Re: 2014 - International year of crystallography: for example, pyrite. |
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I would like to contribute to this interesting thread showing a pyrite crystal from Merelani Hills, Manyara, Tanzania. It is a complex crystal combining pyritohedron, octahedron, cube and trapezohedron (tetragon-trioctahedron) faces.
Mineral: | Pyrite |
Locality: | Merelani Hills, Lelatema Mountains, Simanjiro District, Manyara Region, Tanzania | |
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Dimensions: | 3 x 3 cm. |
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A general view of this crystals. The global configuration approaches an icosahedron, an impossible form for crystals. |
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21444 Time(s) |
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Mineral: | Pyrite |
Locality: | Merelani Hills, Lelatema Mountains, Simanjiro District, Manyara Region, Tanzania | |
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Dimensions: | 2.5 x 2.5 cm. |
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The faces: cube (c), octahedron (o), pyritohedron (p) and trapezohedron=tetragon-trioctahedron (t). |
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An ideal crystallographic scheme for this pyrite. Green cube {100}, blue octahedron {111}, orange pyritohedron {210} and grey trapezohedron {211}. |
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_________________ Pablo Rodríguez Cantos
Λίθον˛ον απεδοκίμασαν˛οι οικοδομουντες |
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Martin Rich
Joined: 15 Aug 2013
Posts: 127
Location: Lower Austria
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Posted: Oct 03, 2014 14:47 Post subject: Re: 2014 - International year of crystallography: for example, pyrite. |
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I want to show an unusual habit of Pyrite. This crystal is extremely elongated. Length: 12 mm, diameter: 0.1 mm, this is a ratio of 1: 120!
Martin
Mineral: | Pyrite, Calcite |
Locality: | Zöchling Quarry, Gaupmannsgraben, Ramsau bei Hainfeld, Mostviertel, Lower Austria, Lower Austria/Niederösterreich, Austria | |
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Dimensions: | FOV about 20 mm |
Description: |
Coll. Martin RichPhoto Harald Schillhammer, NHM Vienna |
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21416 Time(s) |
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Josele
Joined: 10 Apr 2012
Posts: 410
Location: Tarifa, Spain
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Posted: Oct 03, 2014 18:27 Post subject: Re: 2014 - International year of crystallography: for example, pyrite. |
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What a weird pyrite! Sorry for my curiosity, don't want be prying but, how was it identified?
The only other photo of pyrite from the same quarry is quite different!
_________________ Josele |
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Martin Rich
Joined: 15 Aug 2013
Posts: 127
Location: Lower Austria
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Posted: Oct 04, 2014 14:54 Post subject: Re: 2014 - International year of crystallography: for example, pyrite. |
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Hello Josele!
The crystal shown in the image is only visual identified. Ok, not very professional! Another, smaller xl was identified by XRD as pyrite and has a thin coating of Fe-oxides. Such elongated pyrite crystals are rare, but not uncommon in (organic material yielding) limestones like in the Zöchling quarry, Lower Austria. Millerite and silicate minerals as well, like Amphiboles, do not occur in this quarry.
Martin
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Jordi Fabre
Overall coordinator of the Forum
Joined: 07 Aug 2006
Posts: 4904
Location: Barcelona
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Posted: Oct 04, 2014 15:34 Post subject: Re: 2014 - International year of crystallography: for example, pyrite. |
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Another example of elongated Pyrite (analyzed) from Minas da Panasqueira, Portugal
Mineral: | Pyrite with Fluorapatite and Siderite |
Locality: | Minas da Panasqueira, Aldeia de São Francisco de Assis, Covilhã, Castelo Branco, Cova da Beira, Centro, Portugal | |
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Dimensions: | 6.5 × 4.6 × 3.2 cm |
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Main crystal size: 2 × 1.3 cm |
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Josele
Joined: 10 Apr 2012
Posts: 410
Location: Tarifa, Spain
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Posted: Oct 04, 2014 15:52 Post subject: Re: 2014 - International year of crystallography: for example, pyrite. |
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I wonder which forces act to develop so asymmetrical growth in an isometric mineral.
Definitely crystallography is as complex as it is fascinating.
Thanks for your kind explanations.
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Roger Warin
Joined: 23 Jan 2013
Posts: 1178
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Posted: Oct 04, 2014 16:25 Post subject: Re: 2014 - International year of crystallography: for example, pyrite. |
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Hi,
Epitaxy on the same mineral is a parallel-axis growth. Contamination of the surface can prevent the second orderly growth.
Roger.
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prcantos
Site Admin
Joined: 17 Apr 2012
Posts: 243
Location: Granada (Spain)
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Posted: Oct 05, 2014 17:51 Post subject: Re: 2014 - International year of crystallography: for example, pyrite. |
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Diploid-shaped pyrite crystals from Duff Quarry. See https://www.mineral-forum.com/message-board/viewtopic.php?p=11208#11208 .
Mineral: | Pyrite |
Locality: | C. E. Duff & Son Quarry, Huntsville, Logan County, Ohio, USA | |
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Dimensions: | FOV 4 cm. |
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_________________ Pablo Rodríguez Cantos
Λίθον˛ον απεδοκίμασαν˛οι οικοδομουντες |
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prcantos
Site Admin
Joined: 17 Apr 2012
Posts: 243
Location: Granada (Spain)
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Posted: Nov 11, 2014 08:36 Post subject: Re: 2014 - International year of crystallography: for example, pyrite. |
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Another diploid-faced pyrite crystals. It comes from Respina Mine (León, Spain).
In this case we can recognize the diploid faces as half-pentagons on the pyritohedron. The height of this diploid is really low. Home-made measurement gives 175º for the dihedral angle between adjacent trapezoidal faces, which means a {0'098 2 1} ≈ {0'1 2 1} = {1 20 10} form: near a pyritohedron, but in fact a diploid {hkl} with h ≠ k ≠ l ≠ h.
Mineral: | Pyrite |
Locality: | Respina Mine, Fuentes de Respina, Puebla de Lillo, Comarca Valle de Boñar, León, Castile and León, Spain | |
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Dimensions: | 5.5 x 4.5 cm. |
Description: |
Pyrite in talc matrix. A false pyritohedron... |
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Mineral: | Pyrite |
Locality: | Respina Mine, Fuentes de Respina, Puebla de Lillo, Comarca Valle de Boñar, León, Castile and León, Spain | |
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Dimensions: | 4 mm. the front edge |
Description: |
... look at the line dividing the upper pentagon into two trapezoidal halves. They are in fact faces of the diploid. They appear in every 'pentagon' of this crystal, and can be detected mainly because of shining differences. |
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Estimated ideal form for this specimen, a {0'098 2 1} ≈ {0'1 2 1} diploid, not a pyritohedron! |
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_________________ Pablo Rodríguez Cantos
Λίθον˛ον απεδοκίμασαν˛οι οικοδομουντες |
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marco campos-venuti
Joined: 09 Apr 2014
Posts: 207
Location: Sevilla
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Posted: Nov 11, 2014 10:10 Post subject: Re: 2014 - International year of crystallography: for example, pyrite. |
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Josele wrote: | I wonder which forces act to develop so asymmetrical growth in an isometric mineral.
Definitely crystallography is as complex as it is fascinating.
Thanks for your kind explanations. |
That's true Josele, look at this picture. They look as 3 monometric crystals, but only one is isometric. Crystallography is just a human approximation to nature.
-yellow crystal is a Garnet from Imilchil, Morocco
-brown crystal is a Dravite tourmaline crystal from Tomkap tourmaline mine, Yinnietharra, Western Australia
-green crystal is an Epidote crystal from Ras Koh Mts. near Kharan, Balochistan, Pakistan.
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-yellow crystal is a Garnet from Imilchil, Morocco -brown crystal is a Dravite tourmaline crystal from Tomkap tourmaline mine, Yinnietharra, Western Australia -green crystal is an Epidote crystal from Ras Koh Mts. near Kharan, Balochistan, Pakistan |
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Roger Warin
Joined: 23 Jan 2013
Posts: 1178
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Posted: Nov 23, 2014 10:07 Post subject: Re: 2014 - International year of crystallography: for example, pyrite. |
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This pyrite crystal seen in Munich Show was for me the top of “my” International Year of Crystallography. It is a gorgeous crystal.
Roger.
Mineral: | Pyrite |
Locality: | Huanzala Mine, Huallanca District, Dos de Mayo Province, Huánuco Department, Peru | |
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Dimensions: | 7.5 cm |
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20573 Time(s) |
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prcantos
Site Admin
Joined: 17 Apr 2012
Posts: 243
Location: Granada (Spain)
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Posted: Dec 16, 2014 18:10 Post subject: Re: 2014 - International year of crystallography: for example, pyrite. |
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Nanisivik Mine is well known for its pyrite crystals. They show faces according many different crystallographic forms.
In this specimen you can recognize the cube, the octahedron, the dodecahedron, the trapezohedron and the pyritohedron.
Mineral: | Pyrite |
Locality: | Nanisivik Mine, Nanisivik, Baffin Island, Nunavut Territory, Canada | |
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Dimensions: | 3.5 x 2.5 cm. |
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20106 Time(s) |
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Mineral: | Pyrite |
Locality: | Nanisivik Mine, Nanisivik, Baffin Island, Nunavut Territory, Canada | |
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Dimensions: | 1 x 1 cm. crystal |
Description: |
This crystal has cubic, octahedral and dodecahedral faces. The narrow face at the bottom right belongs to the trapezohedron. |
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20112 Time(s) |
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Mineral: | Pyrite |
Locality: | Nanisivik Mine, Nanisivik, Baffin Island, Nunavut Territory, Canada | |
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Dimensions: | FOV 2.5 cm. |
Description: |
Another crystal with adds pyritohedral faces. |
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20118 Time(s) |
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Mineral: | Pyrite |
Locality: | Nanisivik Mine, Nanisivik, Baffin Island, Nunavut Territory, Canada | |
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Dimensions: | FOV 2.5 cm. |
Description: |
Another complex crystal. Can you guess it? |
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20118 Time(s) |
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_________________ Pablo Rodríguez Cantos
Λίθον˛ον απεδοκίμασαν˛οι οικοδομουντες |
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Martin Rich
Joined: 15 Aug 2013
Posts: 127
Location: Lower Austria
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Posted: Dec 30, 2014 15:35 Post subject: Re: 2014 - International year of crystallography: for example, pyrite. |
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The international year of crystallography is still running!
Mineral: | Pyrite, Calcite |
Locality: | Stan Trg (Stari Trg) Mine, Trepča Complex, Trepča Valley, Kosovska Mitrovica, Kosovska Mitrovica District, Kosovo | |
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Dimensions: | 7.5 x 6.5 x 4 cm |
Description: |
Complex aggregate of rounded pyrite crystals. Only {100} is clearly identifiable. New find from 2014. |
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19980 Time(s) |
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