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V-Twin Found in Washington
  
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eric8he




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PostPosted: Feb 01, 2020 23:27    Post subject: V-Twin Found in Washington  

I have found another twin while excavating the rest of the pocket that yielded the Frondel twin I posted a while back. This one resembles a Reichenstein-Grieserntal twin, but the angle is too narrow for either law (around 60 degrees).
What could this possibly be? Are these all coincidences?



IMG_2503.JPG
 Mineral: Quartz
 Locality:
King County, Washington, USA
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IMG_2503.JPG



IMG_2527.jpg
 Mineral: Quartz
 Locality:
King County, Washington, USA
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Top-down view showing alignment of axes as well as one edge.
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IMG_2527.jpg


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Bob Morgan




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PostPosted: Feb 02, 2020 22:20    Post subject: Re: V-Twin Found in Washington  

This might be a Sella Law twin with a c-axis angle of 64 degrees 50 minutes. If so, this is the first and is quite unique. If you are going to Tucson there are a bunch of quartz guys that would like to check it out. I'll be out there tomorrow, and can work out some ways to confirm the angle accurately.
It looks like there might be some exaggerated growth in the notch, but that often happens even with non twins. Also, the larger host crystal is clear enough to see some growth history of the smaller crystal.
Wow!
Bob Morgan
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eric8he




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PostPosted: Feb 02, 2020 22:33    Post subject: Re: V-Twin Found in Washington  

Unfortunately I am not in Tucson and cannot attend. What are some of the next steps to verify if it truly is a twin?
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Bob Morgan




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PostPosted: Feb 03, 2020 11:52    Post subject: Re: V-Twin Found in Washington  

One approach is to set a contact goniometer to the complementary angle of 119 degrees and lay it parallel to the striations of one crystal - both sets on either side of the outer edge. Then see if there is similar alignment with the striations on the other crystal. A carpenters bevel gauge works for this.
In your second photo some misalignment seems to be present between the meeting prism faces. Is there any twist in the smaller crystal to account for that?
Crystal purists want everything square on.
I have a division of my collection of 'close but no cigar' near twins. A review of them, and they help me dampen my hopes and examine more critically.
If you know Rick Dilhoff or Joe George, I expect to see them and show them the technique next week..
I'm hoping this is yet another confirmation of a twin law long undocumented.
Please share a photo of your Frondel twin, and thanks for giving it the designation that law has deserved.

Bob Morgan
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Bob Morgan




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PostPosted: Feb 03, 2020 11:54    Post subject: Re: V-Twin Found in Washington  

My mistake - the complementary angle is 116 degrees.

Bob
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eric8he




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PostPosted: Feb 03, 2020 22:31    Post subject: Re: V-Twin Found in Washington  

Here is the thread with the supposed Frondel-law twin.
https://www.mineral-forum.com/message-board/viewtopic.php?p=68713&highlight=#68713
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eric8he




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PostPosted: Feb 03, 2020 22:49    Post subject: Re: V-Twin Found in Washington  

Bob Morgan wrote:
One approach is to set a contact goniometer to the complementary angle of 119 degrees and lay it parallel to the striations of one crystal - both sets on either side of the outer edge. Then see if there is similar alignment with the striations on the other crystal. A carpenters bevel gauge works for this.
In your second photo some misalignment seems to be present between the meeting prism faces. Is there any twist in the smaller crystal to account for that?
Crystal purists want everything square on.
I have a division of my collection of 'close but no cigar' near twins. A review of them, and they help me dampen my hopes and examine more critically.
If you know Rick Dilhoff or Joe George, I expect to see them and show them the technique next week..
I'm hoping this is yet another confirmation of a twin law long undocumented.
Please share a photo of your Frondel twin, and thanks for giving it the designation that law has deserved.

Bob Morgan


Also to note, the crystals are tapered, which makes it even harder to tell if they are aligned. But one edge pair does seem to match up.
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Reef




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PostPosted: Feb 05, 2020 04:49    Post subject: Re: V-Twin Found in Washington  

In the Sella law twin, the indicated faces of the rhombohedrons must be parallel


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