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Weird face in quartz
  
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Josele




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PostPosted: Nov 25, 2016 18:25    Post subject: Weird face in quartz  

A friend brought me a small smoky quartz from Madagascar, bought in a road shop near Itremo. Although it is somewhat chipped, it retains some interesting features. In addition to the usual faces of the prism (m) and positive (r) and negative (z) rhombohedrons, the crystal shows what I suppose are two faces of the trigonal bipyramid (s), one of the trapezohedron (x) and another one that I can not recognize. Is a small scalene trapezium placed between adjacent x, s, r and m faces as can be seen in pictures.
Comments are welcome!
Thanks.



P1180381.jpg
 Mineral: Quartz (variety smoky)
 Locality:
Itremo Massif, Itremo, Ambatofinandrahana District, Amoron'i Mania Region, Fianarantsoa Province, Madagascar
 Dimensions: 7 cm
 Description:
 Viewed:  3061 Time(s)

P1180381.jpg



P1180398.jpg
 Mineral: Quartz (variety smoky)
 Locality:
Itremo Massif, Itremo, Ambatofinandrahana District, Amoron'i Mania Region, Fianarantsoa Province, Madagascar
 Dimensions: FOV about 2.5 cm
 Description:
s-face
 Viewed:  3055 Time(s)

P1180398.jpg



Q3f.jpg
 Mineral: Quartz (variety smoky)
 Locality:
Itremo Massif, Itremo, Ambatofinandrahana District, Amoron'i Mania Region, Fianarantsoa Province, Madagascar
 Description:
Face at reflex is a x-face. At his right a bigger s-face and over them the unknown face.
 Viewed:  3054 Time(s)

Q3f.jpg



Q4.jpg
 Mineral: Quartz (variety smoky)
 Locality:
Itremo Massif, Itremo, Ambatofinandrahana District, Amoron'i Mania Region, Fianarantsoa Province, Madagascar
 Description:
Trying to reflect on each of the faces.
Last photo shows the weird face at reflex.
 Viewed:  3063 Time(s)

Q4.jpg



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Pete Richards
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PostPosted: Nov 27, 2016 16:43    Post subject: Re: Weird face in quartz  

Josele, you offer quite a puzzle! I think things are not as they seem, though I can't be sure. I note that the face that is in position to be the s face actually is not smooth, but concave and stepped - in your top-left image in figure 4 this is particularly apparent. Furthermore, I don't think its relationship to the other faces is right for an s face. The s face has the special property that it bevels rhombohedron and prism faces in both directions. This is to say that its opposite edges are parallel to each other in both directions, as can be seen in my first drawing and your second (excellent) image. I don't think the face in your fourth image shows this property, and I propose to ignore it as being not a true face, though I don't have a good explanation for why it is there. Perhaps contact with another crystal?

I suggest that there is no s face on this corner, and that the face illuminated in your figure 3 is an x face with indices (511). The mystery face appears to bevel x(511) and r(101). If so, its indices must be some linear combination of (511) and (101). I chose (511)+2*(101) or (713), which I arbitrarily named ∂. (713) is not a satisfying set of indices because they are too high (especially 7), but I don't think any combination of the indices of the two surrounding faces (i.e. (511) and (101) ) will produce a face that bevels the two and has satisfyingly low indices.

Further progress beyond this somewhat speculative analysis would require measurement of the angles between the various faces.

Hopefully this analysis is of some help in understanding your crystal!



quartz.jpeg
 Description:
 Viewed:  2865 Time(s)

quartz.jpeg



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Pierre Joubert




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PostPosted: Nov 28, 2016 02:56    Post subject: Re: Weird face in quartz  

'Perhaps contact with another crystal? '

That is what it looks like to me too.

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PostPosted: Nov 28, 2016 19:02    Post subject: Re: Weird face in quartz  

Pete, Pierre, thanks for your help.

After seeing Peter's drawings and spent some more time with the X10 loupe, now I see there is not a s-face in this corner as you pointed, definitely angles don't fit. Although to me it does not seem a contact rather a complex / distorted step followed by a slightly curved plane sub-parallel to the adjacent r-face. There is some other distorted corners at this specimen. Anyway, not a real face.

The supposed x-face really looks like a true x-face. Face is flat but it has the longest side of the triangle somewhat curve because prism face is curved at top.

And weird small face is a bevel between x and r faces, as showed in Peter's figures 4 and 5. Not a very common face!

Pete, I really envy your capability for recognizing faces and even for determining Miller indices (from photos!!!), congratulations and thanks for your patience sharing your knowledge in this didactic and profitable way.



P1180448.jpg
 Mineral: Quartz
 Locality:
Itremo Massif, Itremo, Ambatofinandrahana District, Amoron'i Mania Region, Fianarantsoa Province, Madagascar
 Dimensions: FOV: 2 cm
 Description:
 Viewed:  2723 Time(s)

P1180448.jpg



P1180442.jpg
 Mineral: Quartz
 Locality:
Itremo Massif, Itremo, Ambatofinandrahana District, Amoron'i Mania Region, Fianarantsoa Province, Madagascar
 Dimensions: FOV: 2 cm
 Description:
A s-face in attached smaller crystal and another one back out of focus
 Viewed:  2724 Time(s)

P1180442.jpg



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PostPosted: Nov 29, 2016 03:16    Post subject: Re: Weird face in quartz  

Hi Josele. May I make a suggestion to you and the administrators? There has been a number of threads about curious growth patterns and shapes in quartz. Can we not build on this thread and slightly change the topic to accommodate other contributions, as well as with links to all previous contributions? I also have a number of 'strange' forms of quartz to show.
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PostPosted: Nov 29, 2016 10:57    Post subject: Re: Weird face in quartz  

Pierre, of course you can use this thread to show your weird quartz when you want. I'm already looking forward to see them!
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PostPosted: Nov 29, 2016 11:36    Post subject: Re: Weird face in quartz  

Josele wrote:
Pierre, of course you can use this thread to show your weird quartz when you want. I'm already looking forward to see them!


Fantastic! Thank you Josele. I will do so when time allows:-)

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PostPosted: Nov 29, 2016 12:08    Post subject: Re: Weird face in quartz  

Pierre Joubert wrote:
Hi Josele. May I make a suggestion to you and the administrators? There have been a number of threads about curious growth patterns and shapes in quartz. Can we not build on this thread and slightly change the topic to accommodate other contributions, as well as with links to all previous contributions? I also have a number of 'strange' forms of quartz to show.


Hi Pierre!,

I take the liberty to speak as the FMF administrators team. It is a great suggestion and following the very good response from Josele, of course go ahead and publish your quartz crystals with strange shapes or difficult to explain faces. It will convert the thread in a very interesting crystal morphology lesson.

Fortunately, It is not necessary to change anything: the thread is in the right topic (minerals and mineralogy) and it can directly incorporate other specimens with similar questions. I said fortunately, because certain changes involve an overwhelming load of work for the staff's availability (who work as volunteers) and are very delicate for the structure of the forum. The title of the thread, instead, could be changed to accommodate the plurality of case studies. We'll change it once new specimens join the discussion.

I kindly ask for an effort to maintain the idea of the thread: crystals difficult to explain, as apparently strange faces, weird morphology that could be confused with different crystal systems, or confusing or unique morphological features.
To all readers, please do not convert the thread in a collection of quartz twins, as this is a different topic, or make a mess uploading all quartz groups. The idea is to keep the good level of the discussion and convert it in a good reference for the interpretation of crystal morphology.

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PostPosted: Nov 30, 2016 03:19    Post subject: Re: Weird face in quartz  

Wonderful Cesar. I am looking forward to the expansion of a topic close to my heart. Thank you!
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PostPosted: Dec 07, 2016 14:33    Post subject: Re: Weird face in quartz  

Hi Josele and other interested FMF members. Here is my first contribution, a quartz with goethite specimen, which I found about a year ago. There were a few similar specimens from this pocket, but not quite like this one. It has (to me) a very strange growth form, which could be partly the result of a broken and rehealed crystal. I find it hard to show the specimen as I would want to. Some of the smaller edges are rounded.


P1220917.JPG
 Mineral: Quartz with goethite
 Locality:
Ceres, Warmbokkeveld Valley, Witzenberg, Cape Winelands, Western Cape Province, South Africa
 Dimensions: 35 x 28 x 23 mm
 Description:
 Viewed:  2225 Time(s)

P1220917.JPG



P1220919.JPG
 Mineral: Quartz with goethite
 Locality:
Ceres, Warmbokkeveld Valley, Witzenberg, Cape Winelands, Western Cape Province, South Africa
 Dimensions: 35 x 28 x 23 mm
 Description:
Same as above
 Viewed:  2221 Time(s)

P1220919.JPG



P1220920.JPG
 Mineral: Quartz with goethite
 Locality:
Ceres, Warmbokkeveld Valley, Witzenberg, Cape Winelands, Western Cape Province, South Africa
 Dimensions: 35 x 28 x 23 mm
 Description:
Same as above
 Viewed:  2219 Time(s)

P1220920.JPG



P1220921.JPG
 Mineral: Quartz with goethite
 Locality:
Ceres, Warmbokkeveld Valley, Witzenberg, Cape Winelands, Western Cape Province, South Africa
 Dimensions: 35 x 28 x 23 mm
 Description:
Same as above
 Viewed:  2213 Time(s)

P1220921.JPG



P1220926.JPG
 Mineral: Quartz with goethite
 Locality:
Ceres, Warmbokkeveld Valley, Witzenberg, Cape Winelands, Western Cape Province, South Africa
 Dimensions: 35 x 28 x 23 mm
 Description:
Same as above
 Viewed:  2217 Time(s)

P1220926.JPG



P1220928.JPG
 Mineral: Quartz with goethite
 Locality:
Ceres, Warmbokkeveld Valley, Witzenberg, Cape Winelands, Western Cape Province, South Africa
 Dimensions: 35 x 28 x 23 mm
 Description:
Same as above
 Viewed:  2221 Time(s)

P1220928.JPG



P1220932.JPG
 Mineral: Quartz with goethite
 Locality:
Ceres, Warmbokkeveld Valley, Witzenberg, Cape Winelands, Western Cape Province, South Africa
 Dimensions: 35 x 28 x 23 mm
 Description:
Same as above
 Viewed:  2220 Time(s)

P1220932.JPG



P1220934.JPG
 Mineral: Quartz with goethite
 Locality:
Ceres, Warmbokkeveld Valley, Witzenberg, Cape Winelands, Western Cape Province, South Africa
 Dimensions: 35 x 28 x 23 mm
 Description:
Same as above
 Viewed:  2226 Time(s)

P1220934.JPG



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PostPosted: Dec 08, 2016 11:15    Post subject: Re: Weird face in quartz  

Hi Pierre,

Your specimen definitely qualifies as distorted! I think your second image is closest to being in a standard orientation. You may be right that it involves breaking and healing, but it is not clear that this occurred.

I've taken the liberty of capturing your second image and labeling it with the faces I think are present. r and z are the two rhombohedra that normally terminate quartz crystals, faces labeled m belong to the prism. There is no way to tell for sure which rhombohedron is which - I may have them labeled backwards - but it is usually assumed that the rhombohedron r has the larger faces. The hillocks on the top r face are a common growth feature and don't require breakage to explain; the irregular surface of the bottom r face (seen especially in image 4) is more suggestive of a broken and healed surface, but it appears to be in the proper orientation for an r face. Quartz does have a poor cleavage parallel to the rhombohedron which is sometimes the breakage plane when quartz breaks during growth, so it is possible for this to be a broken surface and still have the right orientation for a rhombohedron face.

The illuminated face in image 3 is a prism face, which is shown by the striations.

Attached is a cartoon that shows how your crystal relates to a more normal shape, in my interpretation.



Quartz A.jpeg
 Description:
Pierre's image 2 with faces labeled.
 Viewed:  2153 Time(s)

Quartz A.jpeg



Quartz B.jpeg
 Description:
Transition from typical quartz morphology to Pierre's quartz's distorted morphology
 Viewed:  2157 Time(s)

Quartz B.jpeg



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Josele




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PostPosted: Dec 08, 2016 17:33    Post subject: Re: Weird face in quartz  

Nice piece, Pierre, very interesting. Without the help of Pete I would never arrive to determine the faces.
One rhombohedron much more developed than the other and few visible prism faces. Could it be called almost a pseudo cubic quartz crystal?

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PostPosted: Dec 09, 2016 01:42    Post subject: Re: Weird face in quartz  

Pete Richards wrote:
Hi Pierre,

Your specimen definitely qualifies as distorted! I think your second image is closest to being in a standard orientation. You may be right that it involves breaking and healing, but it is not clear that this occurred.

I've taken the liberty of capturing your second image and labeling it with the faces I think are present. r and z are the two rhombohedra that normally terminate quartz crystals, faces labeled m belong to the prism. There is no way to tell for sure which rhombohedron is which - I may have them labeled backwards - but it is usually assumed that the rhombohedron r has the larger faces. The hillocks on the top r face are a common growth feature and don't require breakage to explain; the irregular surface of the bottom r face (seen especially in image 4) is more suggestive of a broken and healed surface, but it appears to be in the proper orientation for an r face. Quartz does have a poor cleavage parallel to the rhombohedron which is sometimes the breakage plane when quartz breaks during growth, so it is possible for this to be a broken surface and still have the right orientation for a rhombohedron face.

The illuminated face in image 3 is a prism face, which is shown by the striations.

Attached is a cartoon that shows how your crystal relates to a more normal shape, in my interpretation.


Hi Pete. I really appreciate all your effort to analyze this specimen. The crystal form in your sketches is not uncommon from this area, so if there were no interferences, it probably would have ended up looking like that.

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PostPosted: Dec 09, 2016 01:46    Post subject: Re: Weird face in quartz  

Josele wrote:
Nice piece, Pierre, very interesting. Without the help of Pete I would never arrive to determine the faces.
One rhombohedron much more developed than the other and few visible prism faces. Could it be called almost a pseudo cubic quartz crystal?


Hi Josele. We are blessed to have people like Pete on the forum! I realize again and again that there are many factors that can affect crystal growth in a pocket. These factors make crystal growth the interesting topic that it is.

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PostPosted: Dec 09, 2016 05:17    Post subject: Re: Weird face in quartz  

Sorry Pete, my message should have read like this: 'The crystal forms in your first 3 sketches are not uncommon from this area, so if there were no interferences, it probably would have ended up looking like one of those.'
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