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Ru Smith
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Posted: Aug 10, 2013 09:39 Post subject: Quartz c face |
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Rare quartz crystals displaying a c face show evidence of etching. Why does etching produce a flat (though pitted) c face? Who has examples?
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Quartz var amethyst Four Peaks area, Maricopa County, Arizona, USA. 27 mm. |
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Ru Smith
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Posted: Aug 10, 2013 09:44 Post subject: Re: Quartz c face |
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Ametrine from Bolivia, with 3 x 1 mm c face.
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Quartz var ametrine. Anahi Mine, La Gaiba District, Sandoval Province, Bolivia. 68 mm. |
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Ru Smith
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Posted: Aug 10, 2013 09:49 Post subject: Re: Quartz c face |
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Quartz from Diamantina with 2.5 x 1.5 mm c face.
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Quartz. Diamantina, Minas Gerais, Brazil. 55 mm. |
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Quartz. Diamantina, Minas Gerais, Brazil. 55 mm. |
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Quartz. Diamantina, Minas Gerais, Brazil. 55 mm. |
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Quartz. Diamantina, Minas Gerais, Brazil. 55 mm. |
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Pete Richards
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Posted: Aug 10, 2013 10:13 Post subject: Re: Quartz c face |
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I have one example, on an ametrine crystal, and have seen others. The c faces always seem to be pitted, though the reason is not clear. It would be interesting to know if the c faces grow as sharp faces and then are etched, or whether they grow as rough faces in the first place.
_________________ Collecting and studying crystals with interesting habits, twinning, and epitaxy |
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Ru Smith
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Posted: Aug 10, 2013 11:19 Post subject: Re: Quartz c face |
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Thanks Pete,
I have that same question. Since I've never seen a c face on a quartz crystal that's not etched the suspicion would be that the pinacoid is produced during the etching. I'm just wondering if there's a simple explanation for why that would happen.
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Pierre Joubert
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Posted: Aug 10, 2013 12:36 Post subject: Re: Quartz c face |
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Ru Smith wrote: | Thanks Pete,
I have that same question. Since I've never seen a c face on a quartz crystal that's not etched the suspicion would be that the pinacoid is produced during the etching. I'm just wondering if there's a simple explanation for why that would happen. |
Ru, just a thought/question. What about the involvement of another mineral that the quartz grew against, producing the mentioned effect?
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Ru Smith
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Posted: Aug 10, 2013 12:56 Post subject: Re: Quartz c face |
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Agreed, Pierre, that could happen, but in each of the cases shown (and described elsewhere) the face is perpendicular to the c-axis. Hard to see that as a coincidence. Also the Diamantina example shows etching in a broadly similar style (though with varying intensity) on the other faces of the crystal.
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vic rzonca
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Posted: Aug 10, 2013 18:04 Post subject: Re: Quartz c face |
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I wonder if this lab grown quartz could be considered example of the c face?
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Ru Smith
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Posted: Aug 10, 2013 18:55 Post subject: Re: Quartz c face |
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Wow! Looks like it.
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Ru Smith
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Posted: Aug 11, 2013 19:58 Post subject: Re: Quartz c face |
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I just read (Springer Handbook of Crystal Growth) that the c faces in synthetic quartz result from early termination of crystal growth such that the mature form of the crystals is not attained. I had been wondering if relative growth rates in the direction of the c axis were lower in synthetic crystals than in natural, non-seeded ones.
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