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Growth zoning in fluorite
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Ru Smith




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PostPosted: Mar 03, 2013 22:39    Post subject: Growth zoning in fluorite  

Here is a 2 cm interpenetrant fluorite twin from Cambokeels, Co Durham, showing growth zoning. What does such zoning tell us about the evolution of the precipitating solution? How much time is involved? Who else has interesting examples of this?


Fluorite Cambokeels detail.jpg
 Description:
Fluorite on drusy quartz
Cambokeels Mine, Co Durham, 340 level, found 1989.
2 cm crystal twin on 10 cm matrix
 Viewed:  29825 Time(s)

Fluorite Cambokeels detail.jpg


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am mizunaka




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PostPosted: Mar 04, 2013 03:06    Post subject: Re: Growth zoning in fluorite  

.
The Berbes fluorite has subtle zoning present.
The Llamas fluorite is much more distinct.



BerbeFluorite.jpg
 Description:
Fluorite
Berbes Mining area, Ribadesella, Asturias, Spain
7.2 x 7.8 cm
 Viewed:  29768 Time(s)

BerbeFluorite.jpg



LlamasFluorite.jpg
 Description:
Fluorite
Llamas Quarry, Duyos, Caravia District, Asturias, Spain
1.9 x 1.7 cm
 Viewed:  29801 Time(s)

LlamasFluorite.jpg


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VRigatti




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PostPosted: Mar 04, 2013 09:46    Post subject: Re: Growth zoning in fluorite  

Denton Mine, Hardin County, Illinois USA


fluorite and calcite II.jpg
 Description:
Fluorite
Denton Mine, Hardin County, Illinois USA
11 x 10 x 8 cm
 Viewed:  29743 Time(s)

fluorite and calcite II.jpg


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cascaillou




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PostPosted: Mar 04, 2013 13:36    Post subject: Re: Growth zoning in fluorite  

General cause of purple color in fluorite:
https://gemologyproject.com/wiki/index.php?title=Causes_of_color
(link normalized by FMF)
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Ru Smith




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PostPosted: Mar 09, 2013 17:39    Post subject: Re: Growth zoning in fluorite  

Thanks guys, these are all beautiful images.

Here is a subtle zoning in various shades of green from the West Pastures Mine, Weardale.



Fluorite West Pastures 1.jpg
 Description:
Fluorite showing colour zoning
Alison Pocket, West Pasture Mine, Stanhope, Weardale, Co Durham, UK.
Crystals to ca 15 mm on 10 cm matrix.
 Viewed:  29501 Time(s)

Fluorite West Pastures 1.jpg


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Jesse Fisher




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PostPosted: Mar 09, 2013 18:09    Post subject: Re: Growth zoning in fluorite  

Fluorite crystals from the Rogerley Mine occasionally show a sharply defined yellow color zone, which is always restricted to one corner of the cube. Why it is not symmetrical with the cube center is a mystery to me. These zones also vary in the intensity of UV fluorescence from the green section of the crystal.


IMG_7253r.jpg
 Description:
Fluorite
Rogerley Mine, Frosterley, Weardale, North Pennines, Co. Durham, England, UK

2.5 cm across

A crystal showing well developed "yellow corner" color zoning.
 Viewed:  29447 Time(s)

IMG_7253r.jpg



IMG_7254r.jpg
 Description:
Fluorite
Rogerley Mine, Frosterley, Weardale, North Pennines, Co. Durham, England, UK
2.5 cm.

The same crystal in LWUV. Yellow corner section is less fluorescent than the green portion of the crystal.
 Viewed:  29442 Time(s)

IMG_7254r.jpg


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Ru Smith




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PostPosted: Mar 09, 2013 18:34    Post subject: Re: Growth zoning in fluorite  

How amazing, Jesse. The UV image seems to show distinct cubic edges to the yellow zone. It would be good to think up some possible explanations to test, but it's not obvious what to suggest.
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Ru Smith




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PostPosted: Mar 24, 2013 19:22    Post subject: Re: Growth zoning in fluorite  

It's a pity there don't seem to be any more growth bands here to either confirm or deny the idea that the yellow portion is oldest followed by growth to the right and down, but not to the left and up in the view presented in your photo. The Blackdene specimen on the "elongate" thread shows an early core left behind in one corner and I see the same in a transparent Blue Circle crystal, with the early purple core left behind in one corner of the final green cube.
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Jesse Fisher




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PostPosted: Mar 25, 2013 11:24    Post subject: Re: Growth zoning in fluorite  

On many of them there is a thin outer layer of green over they yellow zone at the cube face. If the yellow zones were earlier than the green, the crystal would have had to nuclear in suspension and grow downward toward contact with the matrix. If this were the case, one would expect to find the occasional "floater" crystal showing no point of attachment. These are virtually unknown from the Rogerley (or other North Pennines mines) to my experience.
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Ru Smith




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PostPosted: Mar 26, 2013 18:56    Post subject: Re: Growth zoning in fluorite  

Completely good point, Jesse. My couple of examples (Blackdene, Heights) have the early corner-hugging core on the matrix side of the crystals.
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Ru Smith




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PostPosted: May 03, 2013 22:02    Post subject: Re: Growth zoning in fluorite  

A transparent Hilton penetration twin with warm amber colour and a subtle internal phantom.


Fluorite amber Hilton.jpg
 Description:
Fluorite penetration twin.
Hilton Mine, Cumbria, UK
Cube edge is 22 mm long.
 Viewed:  28471 Time(s)

Fluorite amber Hilton.jpg


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Jesse Fisher




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PostPosted: May 03, 2013 23:14    Post subject: Re: Growth zoning in fluorite  

The LWUV fluorescence of Hilton yellow fluorite is generally fairly week compared to other colors in North Pennines fluorite. Have you checked this one to see if any bands of stronger fluorescence correspond to the purple layers?
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Ru Smith




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PostPosted: May 03, 2013 23:48    Post subject: Re: Growth zoning in fluorite  

hmm. goes to look for UV lamp and fails to find it.
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Ru Smith




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PostPosted: May 04, 2013 22:35    Post subject: Re: Growth zoning in fluorite  

I eventually found the UV lamp and took the following photo (first time I try a UV photo of a mineral). Interesting how the bands in the twin element protruding towards us at the top show so clearly here.


Fluorite UV Hilton.jpg
 Description:
Fluorite.
Hilton Mine, Cumbria, UK.
Cube edge is 22 mm long.
 Viewed:  28217 Time(s)

Fluorite UV Hilton.jpg


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Ru Smith




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PostPosted: May 18, 2013 22:54    Post subject: Re: Growth zoning in fluorite  

This fluorite from the West Pasture Mine is interesting. There's the usual face-parallel growth zoning, but also an unusual rich green internal zone, roughly 1 mm wide extending from close to the centre of the crystal towards an edge of the cube. It's only visible through the face shown in the photo and the opposite face, but not through the side faces. I wonder how that came to be.


Fluorite West Pasture green streak 1.jpg
 Description:
Fluorite, green with growth zoning.
West Pasture Mine, Stanhope, Weardale, Co Durham, UK.
4 cm specimen with cubes to 12 mm on edge.
 Viewed:  27868 Time(s)

Fluorite West Pasture green streak 1.jpg



Fluorite West Pasture green streak 2.jpg
 Description:
Fluorite.
West Pasture Mine, Stanhope, Weardale, Co Durham, UK.
4 cm specimen with cubes to 12 mm on edge.
 Viewed:  27869 Time(s)

Fluorite West Pasture green streak 2.jpg


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colin robinson




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PostPosted: May 30, 2013 04:38    Post subject: Re: Growth zoning in fluorite  

Here is a piece from a location near Stanhope. In more than 45 years of field collecting Weardale fluorites this is probably one of the more extreme examples. Although it is damaged (inevitable with dump material) the green/purple zoning is quite striking.


TNfluzones.jpg
 Description:
fluorite
Stanhope, Weardale, England
2cm on edge
 Viewed:  27609 Time(s)

TNfluzones.jpg


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Ru Smith




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PostPosted: May 30, 2013 20:56    Post subject: Re: Growth zoning in fluorite  

A lovely and striking piece, Colin.

I wonder what the explanation is? Perhaps intermittent deposition of radioactive material on surfaces during crystal development? (as discussed for "Blue John" by Galwey et al. 1979 here:
https://www.minersoc.org/pages/Archive-MM/Volume_43/43-326-243.pdf )
(link normalized by FMF)

Conclusions from that paper are attached.



Conclusions Galwey Jones Reed.jpeg
 Description:
 Viewed:  27530 Time(s)

Conclusions Galwey Jones Reed.jpeg


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Ru Smith




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PostPosted: Jul 27, 2013 13:19    Post subject: Re: Growth zoning in fluorite  

This is an attractive zoned fluorite twin, blue/green to purple, from Blackdene Mine.


Fluorite Blackdene 1.jpg
 Description:
Fluorite, penetration twin. ex Arthur Scoble.
Blackdene Mine, Ireshopeburn, Weardale, North Pennines, Co. Durham, England, UK.
25 mm.
 Viewed:  26535 Time(s)

Fluorite Blackdene 1.jpg


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nurbo




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PostPosted: Jul 27, 2013 15:43    Post subject: Re: Growth zoning in fluorite  

Hi Ru,
What do you make of this? Its got me baffled. I just got it a couple of weeks ago and Ive been thinking about how it formed ever since. Any thoughts on it?



a.jpg
 Description:
Fluorite.
Skears Mine, Teesdale, Co Durham, England, UK.
23 mm across longest edge
 Viewed:  26440 Time(s)

a.jpg



c.jpg
 Description:
Fluorite.
Skears Mine, Teesdale, Co Durham, England, UK.
23 mm across longest edge
 Viewed:  26439 Time(s)

c.jpg


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Ru Smith




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PostPosted: Jul 27, 2013 23:33    Post subject: Re: Growth zoning in fluorite  

This reminds me of Jesse's yellow-cornered green fluorite, nurbo.

The only explanation I can think of is that parallel growth (or near-parallel since High Skears specimens often show subtly curved faces) resulted in a step at the corner of the composite crystal and subsequent precipitation, in crystallographic continuity, then "healed" the step.

The attached photos show some examples of such steps at the corners/edges of composite crystals from the High Skears Mine.



High Skears 1.jpg
 Description:
Fluorite.
High Skears Mine, Middleton-in-Teesdale, Middleton, Co. Durham, England, UK.
Detail of 2 cm composite crystal in 4 cm specimen.
 Viewed:  26440 Time(s)

High Skears 1.jpg



High Skears 2.jpg
 Description:
Fluorite.
High Skears Mine, Middleton-in-Teesdale, Middleton, Co. Durham, England, UK.
Detail of 31 mm composite crystal showing growth zonation.
 Viewed:  26474 Time(s)

High Skears 2.jpg



High Skears 3.jpg
 Description:
Fluorite.
High Skears Mine, Middleton-in-Teesdale, Middleton, Co. Durham, England, UK.
Detail of 31 mm composite crystal showing steps and subtle curvature.
 Viewed:  26417 Time(s)

High Skears 3.jpg



High Skears 4.jpg
 Description:
Fluorite.
High Skears Mine, Middleton-in-Teesdale, Middleton, Co. Durham, England, UK.
Detail of 31 mm composite crystal showing steps and growth zonation.
 Viewed:  26429 Time(s)

High Skears 4.jpg


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