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eric8he
Joined: 13 Oct 2019
Posts: 7
Location: Seattle, Washington
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 Posted: Feb 01, 2020 23:27 Post subject: V-Twin Found in Washington |
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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?
| Mineral: | Quartz |
| Locality: | | King County, Washington, USA |  |
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| 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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12356 Time(s) |
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Bob Morgan
Joined: 18 Jan 2018
Posts: 250
Location: Savannah, Georgia
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| Posted: Feb 02, 2020 22:20 Post subject: Re: V-Twin Found in Washington |
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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
Joined: 13 Oct 2019
Posts: 7
Location: Seattle, Washington
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| Posted: Feb 02, 2020 22:33 Post subject: Re: V-Twin Found in Washington |
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| 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
Joined: 18 Jan 2018
Posts: 250
Location: Savannah, Georgia
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| Posted: Feb 03, 2020 11:52 Post subject: Re: V-Twin Found in Washington |
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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
Joined: 18 Jan 2018
Posts: 250
Location: Savannah, Georgia
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| Posted: Feb 03, 2020 11:54 Post subject: Re: V-Twin Found in Washington |
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My mistake - the complementary angle is 116 degrees.
Bob
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eric8he
Joined: 13 Oct 2019
Posts: 7
Location: Seattle, Washington
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eric8he
Joined: 13 Oct 2019
Posts: 7
Location: Seattle, Washington
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| Posted: Feb 03, 2020 22:49 Post subject: Re: V-Twin Found in Washington |
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| 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
Joined: 13 Dec 2016
Posts: 36
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| Posted: Feb 05, 2020 04:49 Post subject: Re: V-Twin Found in Washington |
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In the Sella law twin, the indicated faces of the rhombohedrons must be parallel
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