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Ru Smith
Joined: 13 Oct 2012
Posts: 362
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Posted: Feb 02, 2013 00:28 Post subject: Complex fluorite crystal forms - (9) |
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I just took this close-up of a Hilton Mine fluorite (reducing the depth of field to avoid the distraction of the internal transparency of the crystal). Who can decipher which forms result in such complex modification of the corners?
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Fluorite Hilton Mine, Scordale, Cumbria, England 1 cm twin on 4.5 cm matrix |
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Roger Warin
Joined: 23 Jan 2013
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Posted: Feb 02, 2013 04:23 Post subject: Re: Complex fluorite crystal forms - (9) |
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Hello,
The cube is truncated by a hexoctahedral form on every corner.
I add a picture in a future post.
Roger.
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Roger Warin
Joined: 23 Jan 2013
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Posted: Feb 02, 2013 05:13 Post subject: Re: Complex fluorite crystal forms - (9) |
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You have a beautiful fluorite and these truncations are not so frequent.
The result of calculation with the Miller indices {137} is put on drawing.
These values are a visual interpretation of the picture. To confirm, it is necessary to measure the dihedral angles between the various faces.
So your fluorite has 54 faces, 56 corners and 108 edges in a single euhedral crystal .
Roger.
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Jesse Fisher
Joined: 18 Mar 2009
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Location: San Francisco
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Posted: Feb 02, 2013 09:27 Post subject: Re: Complex fluorite crystal forms - (9) |
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While modifications to the cube other than twinning are not commonly seen on Northern English fluorites, I have seen hexoctahedral corners on a few other specimens, including one that I have from the Boltsburn Mine. Rare but not unknown.
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J Rafael
Joined: 15 Jan 2011
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Location: Asturias
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Roger Warin
Joined: 23 Jan 2013
Posts: 1179
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Posted: Feb 02, 2013 10:03 Post subject: Re: Complex fluorite crystal forms - (9) |
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Speaking fluorite, here is a well-presented.
Roger.
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Fluorite, quartz, dolomite Hunan, China |
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43651 Time(s) |
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Ru Smith
Joined: 13 Oct 2012
Posts: 362
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Posted: Feb 02, 2013 11:08 Post subject: Re: Complex fluorite crystal forms - (9) |
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Fantastic guys! This definitely adds to my enjoyment of the crystal.
Roger, that is a wonderful summary. What software do you use for the crystal drawing?
I agree with Jesse that these combinations of cubes with hexoctahedra occur elsewhere in this region. I have examples from Seata, Wetgrooves and Great Sleddale in Yorkshire; Burtree Slitts in Weardale and the Diana Vein specimens from Northumberland that we looked at a couple of days ago also show this form.
Delightful specimen from the Emilio Mine J Rafael. Thanks for showing that.
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Roger Warin
Joined: 23 Jan 2013
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Posted: Feb 02, 2013 11:32 Post subject: Re: Complex fluorite crystal forms - (9) |
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I use an older version of Dowty’s SHAPE (1995).
Roger.
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Pete Richards
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Posted: Feb 02, 2013 13:38 Post subject: Re: Complex fluorite crystal forms - (9) |
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Cubes with corners modified by hexoctahedra (specifically {137}) are fairly common in fluorite from northern Ohio. Other cubes are often modified by the trapezohedron {113}, often mistaken for a trisoctahedron since three faces occur where each octahedron face would be. See drawings for subtle distinction.
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Fluorite various localities, northwest Ohio, USA |
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43489 Time(s) |
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_________________ Collecting and studying crystals with interesting habits, twinning, and epitaxy |
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Ru Smith
Joined: 13 Oct 2012
Posts: 362
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Posted: Feb 02, 2013 17:25 Post subject: Re: Complex fluorite crystal forms - (9) |
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That's excellent Pete. Thank you.
I just looked through the fluorites and found some more examples of cubes with hexoctahedra, but also two specimens showing cube with trapezohedron (both from Yorkshire). Most specimens lack these corner modifications.
I'll take some more photos a bit later, but here's one of each.
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Fluorite showing hexoctahedral corner modifications. Clouds Mine, Ravenstonedale, Kirkby Stephen, Cumbria, UK. 5 mm crystal on 5 cm matrix. |
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Fluorite showing trapezohedral corner modifications. Wetgrooves Mine, Askrigg, Wensleydale, N Yorkshire, UK. Crystals to 8 mm on 45 mm matrix. |
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Ru Smith
Joined: 13 Oct 2012
Posts: 362
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Posted: Feb 02, 2013 17:31 Post subject: Re: Complex fluorite crystal forms - (9) |
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and I have found one (just 4 mm across), from Great Sleddale with both hexoctahedron and trapezohedron.
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John Medici
Joined: 02 Mar 2011
Posts: 124
Location: Ohio
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Posted: Feb 02, 2013 22:40 Post subject: Re: Complex fluorite crystal forms - (9) |
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Thanks for the diagrams, Roger and Pete. I'm still learning. Following are a few northwest Ohio modified fluorites. Let me know if I have wrong modification ID. Thanks.
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fluorite Bluffton, Ohio 1 cm tetrahex-trapezohedron modif.? |
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fluorite Auglaize quarry, Junction, Ohio 1.5 cm field of view tetrahex, hexoct modif. ? |
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fluorite with phantoms Auglaize quarry, Junction, Ohio 0.8 cm tetrahex-hexoct ? |
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fluorite Suever Quarry, Delphos, Ohio 0.9 cm dodecahedron modif. These occur often in this quarry, but usually only one pair of cube faces is modified. |
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fluorite Bluffton Stone Co. quarry, Bluffton, Ohio 1 cm trapezohedron-hexoctahedron modif.? Same modification has been found at the upper level in Delphos in the bicolor (yellow/purple) fluorite. |
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Ru Smith
Joined: 13 Oct 2012
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Posted: Feb 02, 2013 22:44 Post subject: Re: Complex fluorite crystal forms - (9) |
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Well look at this! I can see cube, octahedron, trapezohedron and hexoctahedron. There's another form in there too; look at the very subtle bevels at either side of the trapezohedron face at left. Could that be the trisoctahedron?
How many faces, corners and edges do you reckon, Roger?
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Fluorite, detail of the corner of a 4 mm crystal. Great Sled Dale Mine, Keld, Swaledale, North Yorkshire, UK. 4 mm crystal on 3 cm matrix |
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Ru Smith
Joined: 13 Oct 2012
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Posted: Feb 02, 2013 22:50 Post subject: Re: Complex fluorite crystal forms - (9) |
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Lovely specimens, John.
I hadn't seen the tetrahexahedron (double bevel on cube edges) before. I once had some beautiful Naica specimens showing dodecahedral faces, but they've been lost along the way unfortunately.
These complex crystal forms definitely add to the interest.
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Ru Smith
Joined: 13 Oct 2012
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Posted: Feb 02, 2013 22:52 Post subject: Re: Complex fluorite crystal forms - (9) |
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Those subtle bevels can't be the trisoctahedron now I look again, but must be another form.
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John Medici
Joined: 02 Mar 2011
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Location: Ohio
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Posted: Feb 02, 2013 23:47 Post subject: Re: Complex fluorite crystal forms - (9) |
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Sorry, I missed labeling a dodecahedron face, between the tetrahex faces on my Bluffton specimen (my number 006).
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nurbo
Joined: 23 Sep 2008
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Location: Lancashire
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Posted: Feb 03, 2013 07:34 Post subject: Re: Complex fluorite crystal forms - (9) |
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Here is one from the California Mine in Teesdale, it seems these are rare but widespread in the North of England, when I get a chance I'll be checking all my Fluorite's for these modifications, The crystal in the second photo seems to have a further modification which is quite hard to see in the picture so Ive cobbled together a drawing which is inaccurate but shows what it looks like.
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Eggleshope, Teesdale, Co Durham, England, UK. Fluorite to 5 mm |
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Eggleshope, Teesdale, Co Durham, England, UK. Fluorite to 8 mm |
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Ru Smith
Joined: 13 Oct 2012
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Posted: Feb 03, 2013 12:01 Post subject: Re: Complex fluorite crystal forms - (9) |
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Great stuff, nurbo.
So, you have found another example with both trapezohedron and hexoctahedron showing. Do any of yours have a little triangular facet right at the corner (the octahedron)?
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nurbo
Joined: 23 Sep 2008
Posts: 457
Location: Lancashire
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Posted: Feb 03, 2013 13:56 Post subject: Re: Complex fluorite crystal forms - (9) |
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Hi Ru,
If i'm understanding you correctly yes, i've a few with the octahedron,and some Galena's that show it too, Im really glad you started this thread, it made me remember the edges on this one and set me off trying to find it I couldnt remember the locality either, eventually I found it in with the samples I have for trading or giving to people.
a couple of observation's on the California Mine piece ... the Fluorite cube's with the trapezohedral modification are an earlier generation than the the ones with both,trapezohedral and hexoctahedral, i also noticed that the trapezohedral modifications are present on the raised edges on the face of the first generation of cubes as well, when the sun comes back up I'll try and get some better photo's.
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Antonio Alcaide
Site Admin
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Posted: Feb 03, 2013 18:21 Post subject: Re: Complex fluorite crystal forms - (9) |
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Nice complex fluorites. More complexity here https://www.foro-minerales.com/forum/viewtopic.php?p=70706#70706
in Spanish, with deeply complex crystals from Cillargas, Spain (in the link) and Jaimina Mine, Asturias, Spain (more hexoctahedra called hexaquisoctahedra in Europe) as well as tetrahexahedron on a Naica specimen, as Ru commented (see the previous posts).
Regards
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