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GeneralInverse of the Japan law?
18th Dec 2018 23:03 UTCEric He
19th Dec 2018 09:17 UTCHarjo Neutkens Manager
19th Dec 2018 10:36 UTCAlfredo Petrov Manager
19th Dec 2018 17:12 UTCEric He
19th Dec 2018 18:09 UTCRonald J. Pellar Expert
Both 84 degrees and 96 degrees are present!
19th Dec 2018 18:16 UTCJamison K. Brizendine 🌟 Expert
19th Dec 2018 18:35 UTCMichael Sommers
19th Dec 2018 19:07 UTCEric He
19th Dec 2018 20:38 UTCAlfredo Petrov Manager
I don't recall ever seeing a half-twin of the 96 degree habit. Curious.
19th Dec 2018 22:31 UTCDana Morong
Anyhow this reminded me of an article in Mineral News, February 1988, v.2, n.2, pages 7-8: "Is it a twin? Watch out for supplementary angles!" by Lanny R. Ream. He said that most collectors probably identify [Japan Law quartz] twins by recognizing a particular "distinctive" shape or the angle of the axes of the two individuals. . . He also mentioned that this is easy for many twins, once you learn to recognize the habit. The angle is 84º33' . . . but went on to show that if one crystal is sticking out of a shaft, the supplementary angle is 95º27' (supplementary angles add up to 180º). It would be nice if there were some means to reproduce this article on mindat, but I don't know how to do that. I hope the degree symbol comes out - we will soon find out!
20th Dec 2018 16:23 UTCRonald J. Pellar Expert
20th Dec 2018 20:30 UTCMichael Sommers
Is it possible that the Oshigahae mine specimens are twins only on the "84°" sides and not on the "96°" sides? Some of them really seem they are not two-crystal twins ("crosses"), they are 3 crystals twinned twice (one central, two offshoots in opposite directions):
20th Dec 2018 21:09 UTCEric He
21st Dec 2018 17:57 UTCRonald J. Pellar Expert
But any extension of the 84º 33' twin crystal will have a 96º 27' angle with the oghter twin crystal, as stated by Alfredo and shown in my previous photo.
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