View previous topic :: View next topic |
Author |
Message |
Ru Smith
Joined: 13 Oct 2012
Posts: 362
|
Posted: Jul 01, 2013 18:35 Post subject: Re: Spinel twins |
|
|
Meanwhile, inspired by Josele's wooden model, goes to fridge to look for model-making materials. Carrots or cheese?
|
|
Back to top |
|
|
Ru Smith
Joined: 13 Oct 2012
Posts: 362
|
Posted: Jul 01, 2013 20:01 Post subject: Re: Spinel twins |
|
|
Cheese.
Description: |
To the left, fluorite spinel twin, cube-dodecahedron. Naica, Chihuahua, Mexico. 2 cm twin on 7 cm specimen. |
|
Viewed: |
27406 Time(s) |
|
|
|
Back to top |
|
|
Ru Smith
Joined: 13 Oct 2012
Posts: 362
|
Posted: Jul 01, 2013 21:40 Post subject: Re: Spinel twins |
|
|
The penetration twin lacked something in the execution, but the cube and cube-dodecahedral spinel contact twins came out well.
Description: |
Penetration twin of cheese cubes. Not the best execution on this one. |
|
Viewed: |
27444 Time(s) |
|
Description: |
To make a spinel contact twin we need to cut octahedral corners off each cube. |
|
Viewed: |
27367 Time(s) |
|
Description: |
then rotate 60 degrees around the cocktail stick twinning axis and rejoin. |
|
Viewed: |
27446 Time(s) |
|
Description: |
Shaving off the edges gives us a cube-dodecahedral spinel contact twin, remarkably similar to the Naica fluorite twin shown in the thread above. Unfortunately this one fell in the wine before I could take a photo. |
|
Viewed: |
27437 Time(s) |
|
|
|
Back to top |
|
|
prcantos
Site Admin
Joined: 17 Apr 2012
Posts: 243
Location: Granada (Spain)
|
Posted: Jul 02, 2013 14:11 Post subject: Re: Spinel twins |
|
|
Really surprising idea! These are 'gourmet twinnings'...
These examples show that twinning may be studied using abstract geometry which doesn't depend on the crystalline structure.
_________________ Pablo Rodríguez Cantos
Λίθον˛ον απεδοκίμασαν˛οι οικοδομουντες |
|
Back to top |
|
|
Peter Farquhar
Site Admin
Joined: 14 May 2011
Posts: 51
Location: Virginia
|
Posted: Jul 02, 2013 14:31 Post subject: Re: Spinel twins |
|
|
What a great idea for learning about twinning while enjoying a pleasant snack. The opportunities seem endless. Do you recommend any particular cheese?
|
|
Back to top |
|
|
Ru Smith
Joined: 13 Oct 2012
Posts: 362
|
Posted: Jul 02, 2013 19:59 Post subject: Re: Spinel twins |
|
|
Thanks gents. I honestly had fun making and eating these models. The very nice Argentinian Cabernet Sauvignon was also a good accompaniment. I had looked at the 2 year matured Reypenaer cheese, found it a bit too thin, and then decided for a good Viking cheese (Jarlsberg). How about some rutile twin models?
|
|
Back to top |
|
|
Ru Smith
Joined: 13 Oct 2012
Posts: 362
|
Posted: Jul 26, 2013 13:31 Post subject: Re: Spinel twins |
|
|
I found this Cornish sphalerite twin with similarities to the Bulgarian galena twin shown earlier. It shows the 60 degree rotation of one element relative to the other with some partial interpenetration.
Description: |
Sphalerite (Fe-rich) with pyrite and quartz. 600' level, Wheal Jane Mine, Cornwall, England, UK. 23 cm specimen with sphalerite crystals to 33 mm. |
|
Viewed: |
27039 Time(s) |
|
|
|
Back to top |
|
|
Ru Smith
Joined: 13 Oct 2012
Posts: 362
|
Posted: Aug 02, 2013 23:09 Post subject: Re: Spinel twins |
|
|
This Kësterite twin is a tetragonal equivalent of a spinel contact twin. The photos are not as clear as I'd like.
Description: |
Kesterite "spinel contact twin". Xuebaoding Mine, Shuijin Town, Pingwu County, Mianyang City, Sichuan Province, China. 14 mm. |
|
Viewed: |
27030 Time(s) |
|
Description: |
Kesterite "spinel contact twin". Xuebaoding Mine, Shuijin Town, Pingwu County, Mianyang City, Sichuan Province, China. 14 mm. |
|
Viewed: |
26961 Time(s) |
|
Description: |
Kesterite "spinel contact twin". Xuebaoding Mine, Shuijin Town, Pingwu County, Mianyang City, Sichuan Province, China. 14 mm. |
|
Viewed: |
26932 Time(s) |
|
|
|
Back to top |
|
|
Ru Smith
Joined: 13 Oct 2012
Posts: 362
|
Posted: Sep 27, 2013 12:59 Post subject: Re: Spinel twins |
|
|
Greetings all,
I just took another look at the Naica fluorite twin, here orientating it with twinning axis vertical and playing with the lighting to highlight re-entrants. I need to try again given a spare moment, with a bit of image stacking to get more depth of field and highlighting of more faces. Compare with the "cheese model" above!
Description: |
Fluorite twin, side view, twinning axis vertical, composition plane horizontal. Naica, Chihuahua, Mexico. Twin is 2 cm on 7 cm specimen. |
|
Viewed: |
26495 Time(s) |
|
|
|
Back to top |
|
|
Ru Smith
Joined: 13 Oct 2012
Posts: 362
|
Posted: Oct 01, 2013 21:35 Post subject: Re: Spinel twins |
|
|
Here's an interesting cyclic arrangement of spinel twins from Myanmar.
Description: |
Spinel in cyclic array of spinel twins. Mogok, Myanmar. 12 mm across. |
|
Viewed: |
26461 Time(s) |
|
Description: |
Spinel, drawing of repeated cycle of spinel twins Dana, 6th edition, pg 221, attributed to Strüver 1878. |
|
Viewed: |
26328 Time(s) |
|
|
|
Back to top |
|
|
Roger Warin
Joined: 23 Jan 2013
Posts: 1177
|
Posted: Oct 02, 2013 03:37 Post subject: Re: Spinel twins |
|
|
What a beauty, as in textbooks.
Roger.
|
|
Back to top |
|
|
Ru Smith
Joined: 13 Oct 2012
Posts: 362
|
Posted: Oct 03, 2013 22:31 Post subject: Re: Spinel twins |
|
|
Thanks Roger. As usual though it's still not as ideal as in the drawing. Here I've rotated a photo to compare with the old Dana drawing.
Description: |
Spinel in cyclic array of spinel twins. Mogok, Myanmar. 12 mm across. |
|
Viewed: |
26195 Time(s) |
|
|
|
Back to top |
|
|
Ru Smith
Joined: 13 Oct 2012
Posts: 362
|
Posted: Oct 04, 2013 18:32 Post subject: Re: Spinel twins |
|
|
While I have the camera out - a pretty spinel twin of diamond.
Description: |
Diamond, spinel twin. Diamantino, Matto Grosso, Brazil. 6 mm |
|
Viewed: |
26123 Time(s) |
|
|
|
Back to top |
|
|
Don Lum
Joined: 03 Sep 2012
Posts: 2858
Location: Arkansas
|
Posted: Oct 04, 2013 21:59 Post subject: Re: Spinel twins |
|
|
Beautiful diamond, Ru. I like it.
_________________ hogwild |
|
Back to top |
|
|
prcantos
Site Admin
Joined: 17 Apr 2012
Posts: 243
Location: Granada (Spain)
|
Posted: Jun 23, 2014 15:45 Post subject: Re: Spinel twins |
|
|
This is a limburgite specimen showing some zeolite micro cystals in vugs: you can see a spinel-twinned faujasite crystal below a sharp octahedron, and some tiny offretite crystals on a spherical mineral (probably phillipsite or hyalite).
Description: |
Faujasite, offretite Limberg Quarries, Sasbach, Kaiserstuhl, Baden-Württemberg, Germany 150X |
|
Viewed: |
24071 Time(s) |
|
_________________ Pablo Rodríguez Cantos
Λίθον˛ον απεδοκίμασαν˛οι οικοδομουντες |
|
Back to top |
|
|
|