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Ru Smith
Joined: 13 Oct 2012
Posts: 362
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Posted: Mar 03, 2013 22:39 Post subject: Growth zoning in fluorite |
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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?
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Fluorite on drusy quartz Cambokeels Mine, Co Durham, 340 level, found 1989. 2 cm crystal twin on 10 cm matrix |
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am mizunaka
Joined: 09 Apr 2010
Posts: 2061
Location: USA
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Posted: Mar 04, 2013 03:06 Post subject: Re: Growth zoning in fluorite |
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The Berbes fluorite has subtle zoning present.
The Llamas fluorite is much more distinct.
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Fluorite Berbes Mining area, Ribadesella, Asturias, Spain 7.2 x 7.8 cm |
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Fluorite Llamas Quarry, Duyos, Caravia District, Asturias, Spain 1.9 x 1.7 cm |
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VRigatti
Joined: 19 Dec 2009
Posts: 81
Location: Denver, CO
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Posted: Mar 04, 2013 09:46 Post subject: Re: Growth zoning in fluorite |
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Denton Mine, Hardin County, Illinois USA
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Fluorite Denton Mine, Hardin County, Illinois USA 11 x 10 x 8 cm |
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44780 Time(s) |
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cascaillou
Joined: 27 Nov 2011
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Ru Smith
Joined: 13 Oct 2012
Posts: 362
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Posted: Mar 09, 2013 17:39 Post subject: Re: Growth zoning in fluorite |
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Thanks guys, these are all beautiful images.
Here is a subtle zoning in various shades of green from the West Pastures Mine, Weardale.
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Fluorite showing colour zoning Alison Pocket, West Pasture Mine, Stanhope, Weardale, Co Durham, UK. Crystals to ca 15 mm on 10 cm matrix. |
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Jesse Fisher
Joined: 18 Mar 2009
Posts: 629
Location: San Francisco
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Posted: Mar 09, 2013 18:09 Post subject: Re: Growth zoning in fluorite |
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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.
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Fluorite Rogerley Mine, Frosterley, Weardale, North Pennines, Co. Durham, England, UK
2.5 cm across
A crystal showing well developed "yellow corner" color zoning. |
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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. |
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Ru Smith
Joined: 13 Oct 2012
Posts: 362
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Posted: Mar 09, 2013 18:34 Post subject: Re: Growth zoning in fluorite |
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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
Joined: 13 Oct 2012
Posts: 362
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Posted: Mar 24, 2013 19:22 Post subject: Re: Growth zoning in fluorite |
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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
Joined: 18 Mar 2009
Posts: 629
Location: San Francisco
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Posted: Mar 25, 2013 11:24 Post subject: Re: Growth zoning in fluorite |
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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
Joined: 13 Oct 2012
Posts: 362
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Posted: Mar 26, 2013 18:56 Post subject: Re: Growth zoning in fluorite |
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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
Joined: 13 Oct 2012
Posts: 362
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Posted: May 03, 2013 22:02 Post subject: Re: Growth zoning in fluorite |
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A transparent Hilton penetration twin with warm amber colour and a subtle internal phantom.
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Fluorite penetration twin. Hilton Mine, Cumbria, UK Cube edge is 22 mm long. |
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Jesse Fisher
Joined: 18 Mar 2009
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Location: San Francisco
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Posted: May 03, 2013 23:14 Post subject: Re: Growth zoning in fluorite |
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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
Joined: 13 Oct 2012
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Posted: May 03, 2013 23:48 Post subject: Re: Growth zoning in fluorite |
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hmm. goes to look for UV lamp and fails to find it.
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Ru Smith
Joined: 13 Oct 2012
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Posted: May 04, 2013 22:35 Post subject: Re: Growth zoning in fluorite |
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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.
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Fluorite. Hilton Mine, Cumbria, UK. Cube edge is 22 mm long. |
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Ru Smith
Joined: 13 Oct 2012
Posts: 362
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Posted: May 18, 2013 22:54 Post subject: Re: Growth zoning in fluorite |
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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.
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Fluorite, green with growth zoning. West Pasture Mine, Stanhope, Weardale, Co Durham, UK. 4 cm specimen with cubes to 12 mm on edge. |
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Fluorite. West Pasture Mine, Stanhope, Weardale, Co Durham, UK. 4 cm specimen with cubes to 12 mm on edge. |
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colin robinson
Joined: 29 May 2013
Posts: 82
Location: Cumbria
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Posted: May 30, 2013 04:38 Post subject: Re: Growth zoning in fluorite |
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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.
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fluorite Stanhope, Weardale, England 2cm on edge |
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Ru Smith
Joined: 13 Oct 2012
Posts: 362
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Posted: May 30, 2013 20:56 Post subject: Re: Growth zoning in fluorite |
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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.
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Ru Smith
Joined: 13 Oct 2012
Posts: 362
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Posted: Jul 27, 2013 13:19 Post subject: Re: Growth zoning in fluorite |
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This is an attractive zoned fluorite twin, blue/green to purple, from Blackdene Mine.
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Fluorite, penetration twin. ex Arthur Scoble. Blackdene Mine, Ireshopeburn, Weardale, North Pennines, Co. Durham, England, UK. 25 mm. |
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nurbo
Joined: 23 Sep 2008
Posts: 457
Location: Lancashire
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Posted: Jul 27, 2013 15:43 Post subject: Re: Growth zoning in fluorite |
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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?
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Fluorite. Skears Mine, Teesdale, Co Durham, England, UK. 23 mm across longest edge |
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Fluorite. Skears Mine, Teesdale, Co Durham, England, UK. 23 mm across longest edge |
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Ru Smith
Joined: 13 Oct 2012
Posts: 362
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Posted: Jul 27, 2013 23:33 Post subject: Re: Growth zoning in fluorite |
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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.
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Fluorite. High Skears Mine, Middleton-in-Teesdale, Middleton, Co. Durham, England, UK. Detail of 2 cm composite crystal in 4 cm specimen. |
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Fluorite. High Skears Mine, Middleton-in-Teesdale, Middleton, Co. Durham, England, UK. Detail of 31 mm composite crystal showing growth zonation. |
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Fluorite. High Skears Mine, Middleton-in-Teesdale, Middleton, Co. Durham, England, UK. Detail of 31 mm composite crystal showing steps and subtle curvature. |
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Fluorite. High Skears Mine, Middleton-in-Teesdale, Middleton, Co. Durham, England, UK. Detail of 31 mm composite crystal showing steps and growth zonation. |
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