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Gerhard Niklasch
Joined: 27 Mar 2009
Posts: 134
Location: Munich
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Posted: Apr 19, 2010 16:20 Post subject: Re: Naica Mine - (11) |
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Many thanks for the illuminating diagrams!
Yeah, I had been struggling with the identification for quite a while, and had to throw away several wrongly annotated pictures before coming up with the above.
(Never trust a mathematician who embarks on actual calculation!)
Perhaps it's just me - I'm finding finding myself even more readily confused when these forms modify an octahedron rather than a cube...
Cheers, Gerhard
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Peter Megaw
Site Admin
Joined: 13 Jan 2007
Posts: 963
Location: Tucson, Arizona
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Posted: Apr 19, 2010 16:47 Post subject: Re: Naica Mine - (11) |
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Pete...taking this one step further. Apologizing in advance for the picture...here's a close up of a trapezohedron on a Naica fluorite...modified by a face that cuts off its triple junction. There would be 6 of these in the form, negative octahedron or negative cube...or something else altogether?
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35202 Time(s) |
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Peter Megaw
Site Admin
Joined: 13 Jan 2007
Posts: 963
Location: Tucson, Arizona
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Posted: Apr 19, 2010 16:51 Post subject: Re: Naica Mine - (11) |
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A few more nica Naica fluorites!
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35228 Time(s) |
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Pocket mate of Gerhard's specimen...6 cm across |
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35227 Time(s) |
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Naica spinel twinned fluorite...with large enhydro. 8 cm across |
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35276 Time(s) |
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Naica octahedron 10 cm on an axis |
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35223 Time(s) |
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Peter Megaw
Site Admin
Joined: 13 Jan 2007
Posts: 963
Location: Tucson, Arizona
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Posted: Apr 19, 2010 16:54 Post subject: Re: Naica Mine - (11) |
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A break from fluorite...a couple "seldom-seens"
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Pyrite "worms" on quartz 5 cm across |
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35310 Time(s) |
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Calcite on epidote from Naica |
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35257 Time(s) |
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Gerhard Niklasch
Joined: 27 Mar 2009
Posts: 134
Location: Munich
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Posted: Apr 19, 2010 17:05 Post subject: Re: Naica Mine - (11) |
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Peter Megaw wrote: | here's a close up of a trapezohedron on a Naica fluorite...modified by a face that cuts off its triple junction. There would be 6 of these in the form, negative octahedron or negative cube...or something else altogether? |
I think you'll find there are actually eight of these in the form. They belong indeed to an octahedron {111}. I'm not sure whether "negative octahedron" is the correct term (there's only one octahedron under the full symmetry group); but the little triangles are oriented opposite to the full {111} triangles - the trapezohedron cuts off the corners of the latter.
-- And that's a nice Naica gallery you have there!
Cheers, Gerhard
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John S. White
Site Admin
Joined: 04 Sep 2006
Posts: 1295
Location: Stewartstown, Pennsylvania, USA
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Posted: Apr 20, 2010 04:37 Post subject: Re: Naica Mine - (11) |
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An old rule that I remember to help distinguish between the two forms described by Pete is to note the orientation of the Y formed by the faces of the form in the corner of the cube. If the Y is upright, the form is the trapezohedron. If the Y is inverted, we are seeing the trisoctahedron.
_________________ John S. White
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Peter Megaw
Site Admin
Joined: 13 Jan 2007
Posts: 963
Location: Tucson, Arizona
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Posted: Apr 20, 2010 10:07 Post subject: Re: Naica Mine - (11) |
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So...to coin a mnenomic..."Y"es its a Trapezohedron
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javmex2
Joined: 06 Sep 2010
Posts: 120
Location: Chihuahua
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Posted: Mar 08, 2011 15:47 Post subject: Re: Naica Mine - (11) |
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Hi, hope you like this photograph, is a real beauty of Mineral Naica Chihuahua Mexico.
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Naica Chihuahua Mexico. anidrithe, calcite. |
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34368 Time(s) |
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Jordi Fabre
Overall coordinator of the Forum
Joined: 07 Aug 2006
Posts: 4904
Location: Barcelona
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Posted: May 22, 2013 12:10 Post subject: Re: Naica Mine - (11) |
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One new wonderful thread to the Featured Columns of FMF! This time the topic is the Naica Mine (see above)
Please continue developing it, a great mine needs a great thread! ;-)
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Mark Ost
Joined: 18 Mar 2013
Posts: 516
Location: Virginia Beach
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Posted: May 22, 2013 15:01 Post subject: Re: Naica Mine - (11) |
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Beautiful
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Ru Smith
Joined: 13 Oct 2012
Posts: 362
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Posted: May 23, 2013 20:41 Post subject: Re: Naica Mine - (11) |
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Galena pseudohexagonal penetration twins with chalcopyrite.
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Galena and chalcopyrite. Naica, Chihuahua, Mexico. 5 cm specimen with galena twins to 1 cm. |
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32037 Time(s) |
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Ru Smith
Joined: 13 Oct 2012
Posts: 362
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Posted: May 23, 2013 21:04 Post subject: Re: Naica Mine - (11) |
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Gem pseudohexagonal penetration twin of fluorite.
Sulphosalt wires and enhydros are visible through the lustrous smooth dodecahedron and cube faces of the twin. Octahedron and trapezoidal icositetrahedron faces are rough, being composed of numerous tiny stepped cube terminations. Twin boundaries cross the edges of the front octahedral face (see the spinel twins thread for a drawing) and juxtapose dodecahedron (smooth) and icositetrahedron (rough) faces.
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Fluorite gem pseudohexagonal penetration twin. Naica, Chihuahua, Mexico. 22 mm. |
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32175 Time(s) |
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Ru Smith
Joined: 13 Oct 2012
Posts: 362
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Posted: May 23, 2013 21:17 Post subject: Re: Naica Mine - (11) |
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I brought this back as a teenager (travelling the US by Greyhound bus).
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Gypsum. Naica, Chihuahua, Mexico. 16 cm crystal. |
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31990 Time(s) |
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Turbo
Joined: 30 Sep 2009
Posts: 260
Location: Delaware
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Posted: May 23, 2013 21:33 Post subject: Re: Naica Mine - (11) |
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A little Baryte from Naica.
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Baryte Naica Mine, Naica, Mun. de Saucillo, Chihuahua, Mexico 3 x 3 cm
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31995 Time(s) |
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Ru Smith
Joined: 13 Oct 2012
Posts: 362
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Posted: May 23, 2013 21:55 Post subject: Re: Naica Mine - (11) |
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That's lovely. I'd not seen baryte from Naica.
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Carles Curto
Joined: 14 Sep 2006
Posts: 160
Location: Barcelona
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Posted: May 24, 2013 01:03 Post subject: Re: Naica Mine - (11) |
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The end of the eighties and the nineties Barcelona was a good place for Mexican minerals. I add some samples to the FMF background.
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Esfalerite + Fluorite Naica, Saucillo, Chihuahua, Mexico 4,5 x 4,2 x 3,4 cm Twinned crystal on a group of clear octahedral crystals of Fluorite. |
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31851 Time(s) |
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Galena Naica, Saucillo, Chihuahua, Mexico 5,1 x 6,9 x 4,3 cm. Cuboctahedral Galena crystals on matrix, with Quartz and complex crystals of Sphalerite. |
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31837 Time(s) |
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Galena + Calcite Naica, Saucillo, Chihuahua, Mexico 4,6 x 3,7 x 2,2 cm. Irregular aggregate of cuboctahedral crystals on Calcite matrix. |
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31851 Time(s) |
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Fluorite + Galena Gibraltar mine, Naica, Saucillo, Chihuahua, Mexico 5,5 x 6,8 x 4,9 cm. transparent clear green cubic crystals beveled by the dodecahedron, with phantom growths and on matrix, with cuboctahedral Galena crystal. |
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31864 Time(s) |
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Quartz (amethyst) + Sphalerite Naica, Saucillo, Chihuahua, Mexico 7,3 x 5,4 x 3,9 cm. Prismatic crystals partially coated by Calcite and on Sphalerite matrix. Amethyst is not especially common at Naica. |
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31871 Time(s) |
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Anhydrite Maravillas Mine, Naica, Saucillo, Chihuahua, Mexico 6,5 x 4,8 x 3,5 cm. Aggregate of two flattened sky blue crystals partially coated by Calcite. |
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31859 Time(s) |
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Carles Curto
Joined: 14 Sep 2006
Posts: 160
Location: Barcelona
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Posted: May 24, 2013 01:11 Post subject: Re: Naica Mine - (11) |
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And two more (I apologize the quality of the pictures, but I think the samples have interesting characteristics).
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Gypsum Maravillas Mine, Naica, Saucillo, Chihuahua, Mexico 9,8 x 7,5 x 2,2 cm. Two transparent, colerless, doubly terninated crystals, one of them clearly dominant, with a small matrix. |
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31839 Time(s) |
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Gypsum Maravillas Mine, Naica, Saucillo, Chihuahua, Mexico 6,2 x 3,2 x 2,0 cm. Transparent colorless Gypsum crystal, on matrix, with inner dissolution channels conteining mobile bubbles. |
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31881 Time(s) |
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Ru Smith
Joined: 13 Oct 2012
Posts: 362
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Posted: May 24, 2013 22:20 Post subject: Re: Naica Mine - (11) |
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Elegant pieces Carles. I like the sphalerite.
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am mizunaka
Joined: 09 Apr 2010
Posts: 2059
Location: USA
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Posted: May 25, 2013 02:29 Post subject: Re: Naica Mine - (11) |
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Quartz with Pyrite after Pyrrhotite Naica Mine, Naica, Mun. de Saucillo, Chihuahua, Mexico 10 x 6.7 cm |
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31632 Time(s) |
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Ru Smith
Joined: 13 Oct 2012
Posts: 362
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Posted: May 25, 2013 15:38 Post subject: Re: Naica Mine - (11) |
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Fluorite octahedra.
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Fluorite octahedra with calcite and pyrite. Naica, Chihuahua, Mexico. Octahedra to about 15 mm on 11 cm matrix. |
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31546 Time(s) |
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