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Growth zoning in fluorite
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nurbo




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PostPosted: Jul 28, 2013 01:13    Post subject: Re: Growth zoning in fluorite  

Thanks Ru,
I had pondered that but I couldnt think of a reason why the purple cube would stop forming when it reached the extent of the first crystals boundaries. Unless theres some kind of almost epitactic relationship or a very unlikely coincidence.
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prcantos
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PostPosted: Jul 28, 2013 04:29    Post subject: Re: Growth zoning in fluorite  

Hi, Ru! I am delighted with your crystallographical threads! I have some questions concerning these two fluorites before in this thread:

https://www.mineral-forum.com/message-board/viewtopic.php?p=32953#32953

https://www.mineral-forum.com/message-board/viewtopic.php?p=31064#31064

Why can we say that they are indeed twins, or twinned crystals? They both show evident lack of global symmetry. Doesn't this reveal that their crystalline lattices don't fit, which is required for twinning?

Regards!!

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Jesse Fisher




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PostPosted: Jul 28, 2013 04:42    Post subject: Re: Growth zoning in fluorite  

They certainly look like classic penetration twins [111} to me.
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prcantos
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PostPosted: Jul 28, 2013 06:16    Post subject: Re: Growth zoning in fluorite  

Yes, they look like so. But do notice that {111} axis doesn't fit the rotation axis. There is a translation beyond the {111}-rotation, and this leads to a lack of symmetry!
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Ru Smith




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PostPosted: Jul 28, 2013 10:36    Post subject: Re: Growth zoning in fluorite  

The nice thing about your crystal, nurbo, is that the growth banding clearly shows that the purple corner is a late fill of an earlier step. The next increment of growth would wrap around the whole "healed" crystal. Jesse describes ( if I remember right) just such a late "wrap" around his yellow-cornered green crystals from Rogerley.

Thanks Pablo. The angular relations look good on that penetration twin for a 60 degree rotation around [111]. As usual, different faces grow at different rates and we end up with something less ideal than Josele's wooden model, but the angles are good. The closest natural examples to the ideal I have seen have been in a diamond and a loparite.
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James Catmur
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PostPosted: Jul 28, 2013 11:43    Post subject: Re: Growth zoning in fluorite  

I have always been fascinated by this specimen. Not only do the fluorite crystals have a complex form, but also the phantom forms a cross within each crystal, which goes through the center of the edge of each crystal.


Jaimina phantoms.JPG
 Description:
Fluorite
Jaimina mine, Carrales, Caravia District, Asturias, Spain
The crystal is 4cm across
The whole specimen measure 28cm x 14cm and every crystal has this phantom and form
 Viewed:  14255 Time(s)

Jaimina phantoms.JPG


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Ru Smith




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PostPosted: Jul 28, 2013 12:10    Post subject: Re: Growth zoning in fluorite  

Looks like a nice hexoctahedron showing on the edges, James. Do you have some more photos to show the shape of the phantom?
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James Catmur
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PostPosted: Jul 28, 2013 15:16    Post subject: Re: Growth zoning in fluorite  

Ru

Not at the moment, but let me see what I can do

James
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PostPosted: Jul 28, 2013 15:51    Post subject: Re: Growth zoning in fluorite  

I had a go with some image correction to enhance a new photo - the color is not right but you can now see that color band / zoning in both crystals. In person it forms a 100, 010, 001 cross with a band perpendicular to each face, in the center of the face.


jaimina.jpg
 Description:
Fluorite
Jaimina mine, Carrales, Caravia District, Asturias, Spain
Crystal of 4cm
 Viewed:  14231 Time(s)

jaimina.jpg


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Ru Smith




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PostPosted: Jul 29, 2013 21:12    Post subject: Re: Growth zoning in fluorite  

I just saw an article on Sectoral Zoning by John Rakovan that looks very relevant for your specimen, James.
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Ru Smith




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PostPosted: Jul 29, 2013 21:40    Post subject: Re: Growth zoning in fluorite  

And that had me looking again at the West Pasture crystal shown above. In that case the vivid green zone seems to be at a growth sector boundary.
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PostPosted: Jul 30, 2013 05:38    Post subject: Re: Growth zoning in fluorite  

Ru

I found the article and will read it this evening. Looks interesting, based on a quick glance

https://www.cas.miamioh.edu/~rakovajf/WTTW%20Sectoral%20Zoning%20Galley.pdf
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prcantos
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PostPosted: Jul 30, 2013 08:54    Post subject: Re: Growth zoning in fluorite  

Ru Smith wrote:
Thanks Pablo. The angular relations look good on that penetration twin for a 60 degree rotation around [111]. As usual, different faces grow at different rates and we end up with something less ideal than Josele's wooden model, but the angles are good. The closest natural examples to the ideal I have seen have been in a diamond and a loparite.


Thanks, Ru. Good and useful explanation.

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Ru Smith




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PostPosted: Jul 30, 2013 18:03    Post subject: Re: Growth zoning in fluorite  

Hi Pablo.

Attached is a small digression from fluorite - a Russian loparite penetration twin, viewed straight down the twin axis, still not ideal, but getting there.

But now we should probably get back to growth (concentric) and sectoral zoning in fluorites!



Loparite twin.jpg
 Description:
Loparite penetration twin, viewed down twin axis.
Kola Peninsula, Murmanskaja Oblast', Northern Region, Russia.
7 mm.
 Viewed:  13954 Time(s)

Loparite twin.jpg


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Ru Smith




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PostPosted: Aug 02, 2013 16:29    Post subject: Re: Growth zoning in fluorite  

I suppose another way to make a cruciform phantom, James, would be for an early cruciform group of parallel growth cubes (like the one shown in Fig 13 of Peter Megaw's article in Rocks & Minerals, 88, March/April 2013) to be engulfed by continued crystal growth.
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Ru Smith




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PostPosted: Aug 06, 2013 19:08    Post subject: Re: Growth zoning in fluorite  

I tried photographing this one under water (Thanks Phil).


Fluorite zoned Heights.jpg
 Description:
Fluorite.
Heights Quarry, Westgate, weardale, Co Durham, England, UK.
3 cm crystal.
 Viewed:  13716 Time(s)

Fluorite zoned Heights.jpg


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Ru Smith




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PostPosted: Aug 07, 2013 21:02    Post subject: Re: Growth zoning in fluorite  

This is a beautiful, luminous thing, but I'm going to have to try again to capture the colour zoning, from blue-green to dark blue to violet to green to white. It reminds me a bit of the sea off the Cape of Good Hope.


Fluorite Weisseck 1.jpg
 Description:
Fluorite.
"Summit Cleft", Weisseck, Lungau, Salzburg, Austria.
75 mm.
 Viewed:  13648 Time(s)

Fluorite Weisseck 1.jpg



Fluorite Weisseck 2.jpg
 Description:
Fluorite.
"Summit Cleft", Weisseck, Lungau, Salzburg, Austria.
75 mm.
 Viewed:  13615 Time(s)

Fluorite Weisseck 2.jpg



Fluorite Weisseck 3.jpg
 Description:
Fluorite.
"Summit Cleft", Weisseck, Lungau, Salzburg, Austria.
75 mm.
 Viewed:  13641 Time(s)

Fluorite Weisseck 3.jpg



Fluorite Weisseck 4.jpg
 Description:
Fluorite.
"Summit Cleft", Weisseck, Lungau, Salzburg, Austria.
75 mm.
 Viewed:  13631 Time(s)

Fluorite Weisseck 4.jpg



Cape of Good Hope.jpg
 Description:
Cape of Good Hope.
 Viewed:  13665 Time(s)

Cape of Good Hope.jpg


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Don Lum




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PostPosted: Aug 07, 2013 22:00    Post subject: Re: Growth zoning in fluorite  

Ru,

There is a clear similarity.

Don

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James Catmur
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PostPosted: Aug 08, 2013 00:36    Post subject: Re: Growth zoning in fluorite  

Ru

Looking carefully (the bottom left smaller crystal shows this well on the last photo) there is clearly some form of discontinuity/zone boundary running down the centre of each side of the crystal. So maybe if grew with that discontinuity between zones and that is where the colour is more intense?

James
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Ru Smith




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PostPosted: Aug 08, 2013 17:19    Post subject: Re: Growth zoning in fluorite  

Hi Don,

Putting up the photos though I see that the fluorite has more green than that sea. I should have thought of something more tropical.

Here's a view of the reverse of the crystal, whch seems to be a complex contact. It gives an impression of the colour zoning - with plenty of backlighting.



Fluorite Weisseck 5.jpg
 Description:
Fluorite.
"Summit Cleft", Weisseck, Lungau, Salzburg, Austria.
75 mm.
 Viewed:  13588 Time(s)

Fluorite Weisseck 5.jpg


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