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Spinel twins
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Ru Smith




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PostPosted: 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?
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PostPosted: Jul 01, 2013 20:01    Post subject: Re: Spinel twins  

Cheese.


Cheese and wine.jpg
 Description:
To the left, fluorite spinel twin, cube-dodecahedron.
Naica, Chihuahua, Mexico.
2 cm twin on 7 cm specimen.
 Viewed:  26938 Time(s)

Cheese and wine.jpg


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Ru Smith




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PostPosted: 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.


Cheese twin 1.jpg
 Description:
Penetration twin of cheese cubes. Not the best execution on this one.
 Viewed:  26977 Time(s)

Cheese twin 1.jpg



Cheese twin corners.jpg
 Description:
To make a spinel contact twin we need to cut octahedral corners off each cube.
 Viewed:  26901 Time(s)

Cheese twin corners.jpg



Cheese twin 2.jpg
 Description:
then rotate 60 degrees around the cocktail stick twinning axis and rejoin.
 Viewed:  26980 Time(s)

Cheese twin 2.jpg



Cheese twin 4.jpg
 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:  26970 Time(s)

Cheese twin 4.jpg


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prcantos
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PostPosted: 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.

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Peter Farquhar
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PostPosted: 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?
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Ru Smith




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PostPosted: 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?
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Ru Smith




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PostPosted: 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.


Sphalerite twin Cornwall 1.jpg
 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:  26575 Time(s)

Sphalerite twin Cornwall 1.jpg


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Ru Smith




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PostPosted: 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.


Kesterite 1.jpg
 Description:
Kesterite "spinel contact twin".
Xuebaoding Mine, Shuijin Town, Pingwu County, Mianyang City, Sichuan Province, China.
14 mm.
 Viewed:  26562 Time(s)

Kesterite 1.jpg



Kesterite 2.jpg
 Description:
Kesterite "spinel contact twin".
Xuebaoding Mine, Shuijin Town, Pingwu County, Mianyang City, Sichuan Province, China.
14 mm.
 Viewed:  26493 Time(s)

Kesterite 2.jpg



Kesterite 3.jpg
 Description:
Kesterite "spinel contact twin".
Xuebaoding Mine, Shuijin Town, Pingwu County, Mianyang City, Sichuan Province, China.
14 mm.
 Viewed:  26463 Time(s)

Kesterite 3.jpg


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Ru Smith




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PostPosted: 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!



Naica fluorite twin side view.jpg
 Description:
Fluorite twin, side view, twinning axis vertical, composition plane horizontal.
Naica, Chihuahua, Mexico.
Twin is 2 cm on 7 cm specimen.
 Viewed:  26026 Time(s)

Naica fluorite twin side view.jpg


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Ru Smith




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PostPosted: Oct 01, 2013 21:35    Post subject: Re: Spinel twins  

Here's an interesting cyclic arrangement of spinel twins from Myanmar.


Cyclic spinel.jpg
 Description:
Spinel in cyclic array of spinel twins.
Mogok, Myanmar.
12 mm across.
 Viewed:  25983 Time(s)

Cyclic spinel.jpg



Cyclic spinel drawing Dana.jpg
 Description:
Spinel, drawing of repeated cycle of spinel twins
Dana, 6th edition, pg 221, attributed to Strüver 1878.
 Viewed:  25857 Time(s)

Cyclic spinel drawing Dana.jpg


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Roger Warin




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PostPosted: Oct 02, 2013 03:37    Post subject: Re: Spinel twins  

What a beauty, as in textbooks.
Roger.
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Ru Smith




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PostPosted: 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.


Cyclic spinel 2.jpg
 Description:
Spinel in cyclic array of spinel twins.
Mogok, Myanmar.
12 mm across.
 Viewed:  25729 Time(s)

Cyclic spinel 2.jpg


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Ru Smith




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PostPosted: Oct 04, 2013 18:32    Post subject: Re: Spinel twins  

While I have the camera out - a pretty spinel twin of diamond.


Diamond spinel.jpg
 Description:
Diamond, spinel twin.
Diamantino, Matto Grosso, Brazil.
6 mm
 Viewed:  25651 Time(s)

Diamond spinel.jpg


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Don Lum




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PostPosted: Oct 04, 2013 21:59    Post subject: Re: Spinel twins  

Beautiful diamond, Ru. I like it.
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prcantos
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PostPosted: 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).


150X_N0004.jpg
 Description:
Faujasite, offretite
Limberg Quarries, Sasbach, Kaiserstuhl, Baden-Württemberg, Germany
150X
 Viewed:  23605 Time(s)

150X_N0004.jpg



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