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

FMF English Forum is moderated by John S. White and Peter Megaw
 

Spanish message board






Newest topics and users posts
23 Oct-15:39:55 Re: rarest quartz twins with inclined axes c (Marco Campos-venuti)
23 Oct-15:24:52 Re: collection of michael shaw (Crosstimber)
23 Oct-14:10:48 Re: rarest quartz twins with inclined axes c (Reef)
23 Oct-13:33:32 Re: help with identification of rock/mineral (Pete Modreski)
23 Oct-13:26:56 Re: scepters - (1) (Marco Campos-venuti)
23 Oct-13:05:41 Re: rarest quartz twins with inclined axes c (Marco Campos-venuti)
23 Oct-11:20:12 Re: rarest quartz twins with inclined axes c (Reef)
23 Oct-10:46:09 Re: rarest quartz twins with inclined axes c (Reef)
23 Oct-09:55:38 Re: rarest quartz twins with inclined axes c (Reef)
23 Oct-08:29:17 Re: collecting focuses and how they can change (Rweaver)
23 Oct-04:04:35 Re: quartz collecting outings in south africa (Pierre Joubert)
23 Oct-03:36:54 Re: quartz collecting outings in south africa (Pierre Joubert)
23 Oct-00:40:31 Re: collecting focuses and how they can change (Jesse Fisher)
22 Oct-23:30:44 Re: help identify these minerals (stumped!!!) (Profpepper)
22 Oct-21:33:26 Re: collecting focuses and how they can change (Jim Robison)
22 Oct-20:41:12 Re: collecting focuses and how they can change (Turbo)
22 Oct-20:16:18 Re: collecting focuses and how they can change (Rweaver)
22 Oct-19:16:14 Re: collecting focuses and how they can change (Peter Megaw)
22 Oct-19:12:26 Re: collecting focuses and how they can change (Peter Megaw)
22 Oct-18:21:54 Re: franjungle collection (Franjungle)
22 Oct-17:43:49 Re: a mineralogical trip through the states of usa - florida (Turbo)
22 Oct-17:29:22 Re: collecting focuses and how they can change (Turbo)
22 Oct-16:45:00 Re: help with identification of rock/mineral (Mineralien)
22 Oct-16:44:20 Re: collecting focuses and how they can change (Peter Megaw)
22 Oct-16:44:11 Re: a mineralogical trip through the states of usa - illinois (Tobi)

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
34114


The time now is Oct 23, 2017 17:35

Search for a textSearch for a text   

A general guide for using the Forum with some rules and tips
About cyclic twinning - (5)
  Goto page Previous  1, 2, 3, 4, 5, 6, 7  Next
  Index -> Featured Columns of FMF
Like
5


View previous topic :: View next topic  
Author Message

Pete Richards
Site Admin



Joined: 29 Dec 2008
Posts: 556
Location: Northeast Ohio


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Oct 25, 2012 16:04    Post subject: Re: About cyclic twinning - (5)  

A correction: the marcasite cyclic twin (on the previous page) is from Cedarville, Ohio, not Cedarville, Iowa!
_________________
Collecting and studying crystals with interesting habits, twinning, and epitaxy
Back to top
Reply to topic Reply with quote
Like
   

Ru Smith




Joined: 13 Oct 2012
Posts: 362


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Oct 25, 2012 18:14    Post subject: Re: About cyclic twinning - (5)  

Fabulous pictures!
Back to top
Reply to topic Reply with quote
Like
   

Jordi Fabre
Overall coordinator of the Forum



Joined: 07 Aug 2006
Posts: 3930
Location: Barcelona


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Oct 25, 2012 23:20    Post subject: Re: About cyclic twinning - (5)  

Pete Richards wrote:
A correction: the marcasite cyclic twin (on the previous page) is from Cedarville, Ohio, not Cedarville, Iowa!

Fixed

Thank you to everybody for this thread. Great discussion!
Back to top
Reply to topic Reply with quote
Like
   

Ru Smith




Joined: 13 Oct 2012
Posts: 362


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Oct 26, 2012 18:49    Post subject: Re: About cyclic twinning - (5)  

Cassiterite is often seen in geniculate twins, but sometimes there are very interesting cyclics. Here are three examples, from Cornwall, Australia and Bohemia.


Cornwall cassiterite cyclic.jpg
 Description:
Cassiterite, tetragonal dipyramids in 6 member cyclic twin
Cornwall
15 mm
 Viewed:  16580 Time(s)

Cornwall cassiterite cyclic.jpg



Australia cassiterite cyclic 1.jpg
 Description:
Cassiterite, cyclic twin of three geniculates
Copes Creek, Tingha Tinfield, Hardinge County, New South Wales, Australia
2 cm
 Viewed:  16576 Time(s)

Australia cassiterite cyclic 1.jpg



cassiterite cyclic.jpg
 Description:
Cassiterite, 3 member cyclic twin
Horni Slavkov (Schlaggenwald), Karlovy Vary, Bohemia, Czech Republic.
15 mm
 Viewed:  16589 Time(s)

cassiterite cyclic.jpg


Back to top
Reply to topic Reply with quote
Like
   

RutileFox




Joined: 14 May 2011
Posts: 33
Location: California

View user's profile

Send private message

PostPosted: Nov 11, 2012 15:03    Post subject: Re: About cyclic twinning - (5)  

Magic with cyclic twinning

As a magician, I enjoy all forms of illusions – both man-made and natural. Magicians often create illusions for their audience members by forcing them to adopt a particular perspective, whether they realize it or not. Later the magician might change this initial perspective (using a variety of subtle maneuvers) to surprise and delight the audience. Cyclic twins can also reveal big surprises when looked at from multiple perspectives, or different points of view.

The famous mathematician H. M. S. Coxeter was one of the early crystallographers to demonstrate the key role of multiple perspectives in understanding crystal structure and symmetry. Coxeter was also an amateur magician and inspired many of the visual illusions by the Dutch artist M. C. Escher. One of my favorite illustrations is Escher’s 1953 lithograph, “Relativity,” (for copyright purposes, please see the image on the official website at http://www.mcescher.com/Shopmain/ShopEU/facsprints-uk/prints.html In a moment, I’ll suggest an analogy between this Escher drawing and a cyclic twinned rutile.

Escher’s “Relativity” combines three alternate perspectives in one architectural structure where the normal laws of gravity apparently do not apply. In viewing this drawing for the first time, most individuals implicitly adopt one perspective of “up and down.” In rotating the drawing (or otherwise changing their perspective), individuals are then surprised to discover other valid perspectives exist, which may either better explain what they see or add to the contradictions experienced (see Scott McDaniel’s excellent analysis of this artwork at http://www.scottmcd.net/artanalysis/?p=548

(links normalized by FMF)

We’ll now examine a rutile twin (PF-3306) from Natus Farm, near Gamsberg Mountain in the Khomas Region of Namibia.

CAUTION: Please look carefully at each 2-D image in the sequence without jumping ahead; at each step, imagine what the entire specimen looks like in 3-D. Try not to peek at the fifth and last image until the very end.

Please note the images are all of the same mineral specimen taken from five different points of view; the different perspectives (labeled north, west, south, east) in the first four images are generated by rotating the specimen a quarter turn from right to left each time; the last image shows a top-down view of the specimen.

Let us know what you see in this rutile specimen when viewed from multiple perspectives.


Peter Farquhar
Claremont, California
USA



Rutile, Namibia (PF-3306)-north.jpg
 Description:
Rutile (PF-3306)
Natus Farm, Gamsberg Mountain, Khomas Region, Namibia
3.0 x 2.4 x 2.1 cm
Perspective #1 - north
 Viewed:  16430 Time(s)

Rutile, Namibia (PF-3306)-north.jpg



Rutile, Namibia (PF-3306)-west.jpg
 Description:
Rutile (PF-3306)
Natus Farm, Gamsberg Mountain, Khomas Region, Namibia
3.0 x 2.4 x 2.1 cm
Perspective #2 - west
 Viewed:  16485 Time(s)

Rutile, Namibia (PF-3306)-west.jpg



Rutile, Namibia (PF-3306)-south.jpg
 Description:
Rutile (PF-3306)
Natus Farm, Gamsberg Mountain, Khomas Region, Namibia
3.0 x 2.4 x 2.1 cm
Perspective #3 - south.
 Viewed:  16424 Time(s)

Rutile, Namibia (PF-3306)-south.jpg



Rutile, Namibia (PF-3306)-east.jpg
 Description:
Rutile (PF-3306)
Natus Farm, Gamsberg Mountain, Khomas Region, Namibia
3.0 x 2.4 x 2.1 cm
Perspective #4 - east.
 Viewed:  16428 Time(s)

Rutile, Namibia (PF-3306)-east.jpg



Rutile, Namibia (PF-3306)-top.jpg
 Description:
Rutile (PF-3306)
Natus Farm, Gamsberg Mountain, Khomas Region, Namibia
3.0 x 2.4 x 2.1 cm
Perspective #5 - top-down
 Viewed:  16430 Time(s)

Rutile, Namibia (PF-3306)-top.jpg


Back to top
Reply to topic Reply with quote
Like
   

Antonio Alcaide
Site Admin



Joined: 23 Aug 2009
Posts: 314
Location: Spain


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Nov 11, 2012 16:28    Post subject: Re: About cyclic twinning - (5)  

Thank very much, Peter, for your reference to Coxeter and Escher, one of my favourite painters. Now I understand my double interest in Escher and crystallography. Your analogy between "Relativity" and a rutile twin is actually "food for thought".

Regards

_________________
Life is the shortest crystal
Back to top
Reply to topic Reply with quote
Like
   

Ru Smith




Joined: 13 Oct 2012
Posts: 362


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Nov 12, 2012 21:17    Post subject: Re: About cyclic twinning - (5)  

Very enjoyable post. Thank you!

This is what happens when you visit the Escher Museum in Den Haag (attached photo).

In your nice twin I see a "threeling" in one plane which took off into an "attempt" at a "sixling" in a perpendicular plane. The "sixling" shares the character of my "Kipushi"/"Kinyanfumbe" (if such a place actually exists) specimen in having parallel opposing sides (left-right in your image).



Escher museum.jpg
 Description:
 Viewed:  16324 Time(s)

Escher museum.jpg


Back to top
Reply to topic Reply with quote
Like
   

Ru Smith




Joined: 13 Oct 2012
Posts: 362


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Nov 12, 2012 21:30    Post subject: Re: About cyclic twinning - (5)  

By the way, M.C.'s half brother Berend George Escher was a mineralogy professor at Leiden University. He "had some influence on M.C.'s work due to his knowledge of crystallography."
Back to top
Reply to topic Reply with quote
Like
   

RutileFox




Joined: 14 May 2011
Posts: 33
Location: California

View user's profile

Send private message

PostPosted: Nov 15, 2012 19:21    Post subject: Re: About cyclic twinning - (5)  

Thanks to Ru Smith for the delightful photo from the Escher Museum. It seems the handsome children on the left side of the room are much taller than the folks on the right.

This so-called “Ames room illusion” can occur when a trapezoidal shaped room secretly replaces the familiar rectangular room. By controlling other perceptual cues, the Ames room seems normal, while more distant objects on the right appear smaller than closer objects of the same size positioned on the left.

For fun, mineral collectors might consider using the Ames illusion to change the sizes of their mineral specimens. For example, larger specimens could be made to appear the size of miniature or thumbnail specimens when positioned appropriately in an Ames (trapezoidal) case rather than in the conventional rectangular display case. Imagine if all your specimens could look exactly the same size! Of course, this innovation in display case construction technology might affect the rules for future competitions.

On the other hand, collectors might be more interested in making their mineral specimens appear larger than life. Like the Ames illusion, the principle of forced perspective could be applied to achieve the desired growth in specimen size.

For instance, the photo below shows a proud Pennsylvania farmer showing off the giant cyclic twinned rutile specimen he recovered when plowing his field near Parkesburg. (This farmer also reportedly grows huge, record-breaking pumpkins in the same fields; it must be the special fertilizer he uses.)

Enjoy.

Peter Farquhar
Claremont, California
USA



GiantRutile.jpg
 Description:
Rutile sixling (PF-3277)
Parkesburg, Sadsbury Township, Chester County, Pennsylvania, USA
5.5 x 5.5 x 5.0 cm
A remarkably large, well formed rutile sixling from Parkesburg (photographed beside a small farmer).
 Viewed:  16229 Time(s)

GiantRutile.jpg


Back to top
Reply to topic Reply with quote
Like
   

Antonio Alcaide
Site Admin



Joined: 23 Aug 2009
Posts: 314
Location: Spain


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Nov 15, 2012 20:02    Post subject: Re: About cyclic twinning - (5)  

Suggestive!!

My humble contribution to this approach to Escher universe. A link to the Parque de las Ciencias (Science Museum) exhibition in my city, Granada (Spain): M. C. Escher: Infinite Universes.

http://www.eschergranada.com/es/exposicion/ambitos
(link normalized by FMF)

Regards

_________________
Life is the shortest crystal
Back to top
Reply to topic Reply with quote
Like
   

Pete Richards
Site Admin



Joined: 29 Dec 2008
Posts: 556
Location: Northeast Ohio


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Nov 15, 2012 21:33    Post subject: Re: About cyclic twinning - (5)  

Well, this thread is getting a bit chaotic as well as distorted (though fun). I will just add that all fishermen always hold their catch at arm's length from their body when a picture is being made. The fish appears huge, but so do the fingers holding it!

I will spare you a picture of my most recent catch!

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

RutileFox




Joined: 14 May 2011
Posts: 33
Location: California

View user's profile

Send private message

PostPosted: Nov 26, 2012 15:51    Post subject: Re: About cyclic twinning - (5)  

Returning to the origins of this thread, I’d like to explore the criteria for a three-sided specimen to be a cyclic twin (i.e., a three-ling or trilling). I’m especially interested in triangular specimens – what we earlier called a “closed loop” – rather than partial sixlings with three sides completed (an "open loop"), or geniculated twins with three sides not forming a loop ("no loop").

For example, the rutile crystal on the specimen pictured below (PF-2123) has been described as “a rare contact twin of triangular aspect” (see the caption for figure 23 in Robert Cook’s article on “The Mineralogy of Graves Mountain, Lincoln County, Georgia” in the Mineralogical Record, volume 16, November-December 1985).

This article also mentions, “Graves Mountain rutile is morphologically complex. … Eightlings are common, as are sixlings. … Fourlings and trillings are less common.”

So here’s my question. What is the difference between a rutile twin of “triangular aspect” and a trilling?

Furthermore, I’m curious to see if anyone has closed-loop examples of trillings or fourlings to share on FMF?

Peter Farquhar
Claremont, California
USA



Rutile - triangular crystal (PF-2123).jpg
 Description:
Rutile (PF-2123)
Graves Mountain, Lincoln County, Georgia USA
5.1 x 4.4 x 3.9 cm
Rutile crystal on a matrix of iron oxide coated kyanite from Graves Mountain, Georgia. The main crystal is 1.9cm on each side of the equilateral triangle.
 Viewed:  15916 Time(s)

Rutile - triangular crystal (PF-2123).jpg


Back to top
Reply to topic Reply with quote
Like
   

Pete Richards
Site Admin



Joined: 29 Dec 2008
Posts: 556
Location: Northeast Ohio


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Nov 28, 2012 09:47    Post subject: Re: About cyclic twinning - (5)  

The morphology of rutile from Graves Mountain is complex indeed! And untwinned crystals are definitely the exception. I'm not sure I understand the morphology of Peter's triangular crystal, so will refrain from an opinion about whether it is a trilling or not.

I have several twins from Graves Mountain which have a morphology vaguely like gypsum crystals. A number of years ago (1996, in fact) I spent quite a bit of time puzzling over them, and eventually figured them out, sort of. Amazingly, I still have the files and can still open them!

These crystals appear to basically be contact twins with one side much larger than the other. The main flat faces are composed of faces of {100} belonging to both individuals; these faces are co-planar (in theory) or nearly so (in reality).

Attached are several diagrams to try to show how these twins are put together. The first shows an ideal twin on {101} of a crystal of this habit. The next drawing shows the distortions that are seen on the actual twin - the left individual is greatly reduced and the prism is complete gone on the top. Note the characteristic deflection where the prism faces of the right individual meet the termination faces of the left individual. Some of the faces of the right crystal are greatly reduced or eliminated, leading to the "monoclinic" appearance.

But there's more. When you look at the end of the right-hand individual, there is a characteristic thin slice along the mid-line which does not quite fit the rest of the crystal. This can be interpreted as a little slice of the left-hand crystal, and in fact thin sections show a thin layer running the length of the crystal, though it often does not show at the surface except at the end. Thus there are only two individuals involved in this twin, and it combines aspects of contact and penetration twinning in a most novel way.

I believe this little misfit encourages rapid nucleation of new crystal growth, causing the distortion to "monoclinic" symmetry.

I also have examples of similar morphology from the Champion Mine, Mono County, California, again with the little wedge at the end of the elongated point.

This relates to Peter's triangular crystal in the following way. Both have major flat faces with a thin line visible parallel to one edge. This is the contact plane for the twin. I think a morphology like Peter's triangular crystal could be developed from my drawings by further selective distortion, but I do not know why it would happen. Perhaps Peter's crystal involves three individuals rather than two.



IMG_3875b.jpg
 Description:
Rutle (twin)
Graves Mountain, Lincolnton County, Georgia, USA
RPR Specimen #1342
Twin is 2 cm across
 Viewed:  15826 Time(s)

IMG_3875b.jpg



rutile sketch 1.jpg
 Description:
Sketches of rutile twin showing mode of distortion
 Viewed:  15857 Time(s)

rutile sketch 1.jpg



rutile sketch 2.jpg
 Description:
The mysterious little sliver at the right end of the pointed crystal.
 Viewed:  15835 Time(s)

rutile sketch 2.jpg



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

RutileFox




Joined: 14 May 2011
Posts: 33
Location: California

View user's profile

Send private message

PostPosted: Dec 02, 2012 22:37    Post subject: Re: About cyclic twinning - (5)  

Thanks to Pete Richards for his most recent post on twinning in Graves Mountain rutiles. I appreciate the time and skill needed to put together such an instructive discussion with great photos and diagrams.

In particular, Pete's last diagram on the “mysterious little sliver” hit home with me -- by illustrating the subtle difficulties in really understanding twinning. As a result, I’m reviewing a number of specimens in my collection to reconsider what twinning is actually occurring. As Pete mentioned earlier, it’s a long, twisted road.

For fun, the photo below shows another cyclic twinned rutile (PF-2655) from Graves Mountain, Georgia. From the side, the specimen has the familiar zig-zag profile of a rutile eightling (like the one (PF-2965) I posted earlier). The top-down view shown in the photo, however, reveals a much more complex twinning. I’ll pass for now on figuring this one out, but it's fun to try.

Meanwhile, please let me know if anyone has photos of closed-loop trillings or fourlings. I have seen a few and am very interested in seeing others.

Peter Farquhar
Claremont, California
USA



Rutile cyclic twin (PF-2655) .jpg
 Description:
Rutile cyclic twin (PF-2655)
Graves Mountain, Lincoln County, Georgia, USA
2.5 x 2.3 x 2.2 cm.
A complex 1.8 cm cyclic twin rutile crystal found on January 12, 1997 by Terry Ledford and Jean Tipton in the front quarry of Graves Mountain. (PF-2655)
 Viewed:  15699 Time(s)

Rutile cyclic twin (PF-2655) .jpg


Back to top
Reply to topic Reply with quote
Like
   

Duncan Miller




Joined: 25 Apr 2009
Posts: 104
Location: Cape Town


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Dec 03, 2012 11:34    Post subject: Re: About cyclic twinning - (5)  

I have posted a photo of this specimen and its description along with an article about its locality before, but as I don't know how to link to another part of the forum, here is a repeat.

Illustration of the formation of a complex polycyclic twin in adularia feldspar. A: Diagram of an idealised monoclinic adularia single crystal viewed obliquely from the right, showing the narrow side pinacoid b, the broad prism faces m, the basal pinacoid c, and the second-order pinacoid x. B: Diagram of the adularia crystal viewed from the side, showing the crystallographic axes. The c-axis is vertical, the b-axis emerges perpendicularly from the page, while the a-axis is inclined by 116º to the vertical plane bearing the b and c-axes. The basal pinacoid c is parallel to the inclined a-axis, and the prism faces m and side pinacoid b are parallel to the vertical c-axis. C: Drawing of the adularia single crystal viewed obliquely from the right, showing the approximate trace of the {021} Baveno twin plane, as a thick line, on the crystal faces. The right hand portion of the crystal is mirror reflected through the twin plane to produce the pyramidal twin illustrated in D, viewed from above. Polycyclic twinning, involving four twin pairs like those in D, can be visualised as four-fold rotation of the Baveno twin around the shared a-axis, represented by the line joining the upper two c faces. This produces the complex cyclic twin sketched in E, viewed from above, from a real example found by Lesley Bust. The corner fishtail grooves can be on either the upper or lower surface, depending on the relative development of the basal pinacoid c and the second-order pinacoid x faces. This particular example also has some evidence of reflection twinning across the {100} plane, parallel to the vertical plane containing both the b and c-axes of the untwinned crystals, so three different twin laws are involved here.

Duncan



Adularia compressed.JPG
 Description:
Adularia
Vredendal Limestone Quarry
10 cm across
 Viewed:  15665 Time(s)

Adularia compressed.JPG



adularia crystals half size.jpg
 Description:
 Viewed:  15646 Time(s)

adularia crystals half size.jpg


Back to top
Reply to topic Reply with quote
Like
   

Jordi Fabre
Overall coordinator of the Forum



Joined: 07 Aug 2006
Posts: 3930
Location: Barcelona


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Dec 03, 2012 11:40    Post subject: Re: About cyclic twinning - (5)  

xenolithos wrote:
I have posted a photo of this specimen and its description along with an article about its locality before, but as I don't know how to link to another part of the forum, here is a repeat...

Here is the link mentioned by Duncan: http://www.mineral-forum.com/message-board/viewtopic.php?p=13160#13160 and here is the link to the post of his article: http://www.mineral-forum.com/message-board/viewtopic.php?p=13335#13335

To know more about the features of this Forum please read: A general guide for using the Forum with some rules and tips
Back to top
Reply to topic Reply with quote
Like
   

RutileFox




Joined: 14 May 2011
Posts: 33
Location: California

View user's profile

Send private message

PostPosted: Dec 15, 2012 16:07    Post subject: Re: About cyclic twinning - (5)  

I enjoyed Duncan’s recent photo of the complex twin of adularia, as well as his detailed analysis and enlightening diagrams that unlock this twinning puzzle. Very nicely done.

In turn, I want to share a rare (unaltered) photo illustrating cyclic twinning in humans. Best wishes for a magical holiday season from the five of us.

Peter



CyclicTwins.jpg
 Description:
Cyclic Twins
Los Angeles, California USA
Rare example of five-fold cyclic twinning in humans captured by John Gaughan at his magic shop in Los Angeles on November 7, 2009.
 Viewed:  15308 Time(s)

CyclicTwins.jpg


Back to top
Reply to topic Reply with quote
Like
   

Pete Richards
Site Admin



Joined: 29 Dec 2008
Posts: 556
Location: Northeast Ohio


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Dec 15, 2012 16:33    Post subject: Re: About cyclic twinning - (5)  

Most remarkable! The individuals of this complex twin are not even in contact with each other - a non-contact fiveling!
_________________
Collecting and studying crystals with interesting habits, twinning, and epitaxy
Back to top
Reply to topic Reply with quote
Like
   

Jordi Fabre
Overall coordinator of the Forum



Joined: 07 Aug 2006
Posts: 3930
Location: Barcelona


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Dec 15, 2012 16:54    Post subject: Re: About cyclic twinning - (5)  

Pete Richards wrote:
...The individuals of this complex twin are not even in contact with each other....

Maybe better.... ;-) ;-)
Back to top
Reply to topic Reply with quote
Like
   

domenico




Joined: 31 Dec 2012
Posts: 28
Location: Garbagnate Mil.-Italy


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Dec 31, 2012 07:36    Post subject: Re: About cyclic twinning - (5)  

My little contribute for this good topic...
Sorry for have only an old "diapositive" digitalyzed but the sample is not in my collection.



Rutile-BARILIcrevola04 BT (DIA).jpg
 Description:
Rutile
Crevoladossola quarries, Ossola Valley-Italy
1 mm
Photo B.Turconi
Colleection P.Barili
 Viewed:  14875 Time(s)

Rutile-BARILIcrevola04 BT (DIA).jpg


Back to top
Reply to topic Reply with quote
Like
   
Display posts from previous:   
   Index -> Featured Columns of FMF   All times are GMT - 5 Hours
Page 4 of 7
  Goto page Previous  1, 2, 3, 4, 5, 6, 7  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 2006-2017


Powered by FMF