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John Betts
Joined: 07 Jun 2012
Posts: 207
Location: New York City
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 Posted: Nov 15, 2012 13:09 Post subject: Basal pinacoid |
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Isn't the term "basal pinacoid" redundant? When describing the termination face of the C-axis would "basal" suffice?
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John Betts |
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gemlover
Joined: 31 Dec 2008
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Location: Easley, SC
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| Posted: Nov 15, 2012 13:36 Post subject: Re: Basal pinacoid |
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Since a "pinacoid" is any pair of parallel crystal faces, basal would describe a particular place/orientation for this pinacoid.
John
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John
John Atwell Rasmussen, Ph.D.. AJP
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arturo shaw
Joined: 23 Oct 2009
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| Posted: Nov 15, 2012 13:40 Post subject: Re: Basal pinacoid |
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Hi John
A pinacoid is not necessarily basal and a "base" could be a pedion for instance and that is not a pinacoid. I'm affraid we need both terms.
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arturo shaw
Joined: 23 Oct 2009
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| Posted: Nov 15, 2012 13:41 Post subject: Re: Basal pinacoid |
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Opsss, almost simultaneous answer :-)
(Boths? well it was Both, sorry...) |
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John Betts
Joined: 07 Jun 2012
Posts: 207
Location: New York City
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| Posted: Nov 15, 2012 13:59 Post subject: Re: Basal pinacoid |
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Thanks.
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Pete Richards
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| Posted: Nov 15, 2012 15:10 Post subject: Re: Basal pinacoid |
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It could be argued that for some symmetry classes the term "basal pinacoid" is redundant. For trigonal bar-3 2/m, the symmetry class of calcite, there is only one pinacoid and it is basal. Hence the term "basal" is unnecessary. But I don't think it really hurts anything to specify it anyway.
Trigonal, hexagonal, and tetragonal symmetry classes that have a mirror plane perpendicular to the unique axis all have this property, that their only pinacoid is basal.
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Antonio Alcaide
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| Posted: Nov 15, 2012 16:04 Post subject: Re: Basal pinacoid |
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| Pete Richards wrote: | | Trigonal, hexagonal, and tetragonal symmetry classes that have a mirror plane perpendicular to the unique axis all have this property, that their only pinacoid is basal. |
Well, I think the trouble for the amateur collector -nearly none of you, who are contributing to this thread- is that we usually forget pinacoid refers to two faces, as John -gemlover- reminded us. This is the reason why I can understand hexagonal symmetry has only one (basal) pinacoid. The tendency -for amateurs I insist- is to consider one of the faces as the pinacoid.
For example, in doubly terminated hanksite crystals -or pyromorphite, mimetite, etc.- I called erroneusly "basal pinacoid" only the face down the crystal. ¿And the other?
I hope to have explained the point well.
Regards.
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