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GeneralInverse of the Japan law?

18th Dec 2018 23:03 UTCEric He

Since the Japan law has an angle of roughly 84 degrees, wouldn't it make sense to have another law as its supplement (96 degrees), as with the case with Reichenstein-Grieserntal twins?

19th Dec 2018 09:17 UTCHarjo Neutkens Manager

I've never seen a 96 degrees twin, and if one would find one the angle would not yet make it a law. For it to be a twinning law the specific twinning has to be common or at least has to have been observed regularly.

19th Dec 2018 10:36 UTCAlfredo Petrov Manager

Wouldn't it then be the same law? Any double-terminated Japan-law twin looks like a cross and displays both the 84 and 96 degree angles, but surely one wouldn't call that 2 different twin laws?

19th Dec 2018 17:12 UTCEric He

Correct. Then it would just be a different form of the same twin, Alfredo. And Harjo, the twinning does not have to be common, as long as contact twinning is proven it is a twin law regardless. An example, as I have stated before, is the Reichenstein-Greiserntal law, which is practically absent in deposits everywhere across the world, except in curious breccia pipes in my state of Washington where they are practically common compared to worldwide deposits, even though there may be less than 100 total collected over 75 years of history.

19th Dec 2018 18:09 UTCRonald J. Pellar Expert

Here is a synthetic Japan Law Twin that illustrates Alfred's point.

Both 84 degrees and 96 degrees are present!

19th Dec 2018 18:16 UTCJamison K. Brizendine 🌟 Expert

When I read the title of the thread, I was thinking of this!

19th Dec 2018 18:35 UTCMichael Sommers

When any "single termination" Japan Law twins are found, are they found with 96 degree angles?

19th Dec 2018 19:07 UTCEric He

That's what I was wondering too. All of them I have seen are 84.33 degrees

19th Dec 2018 20:38 UTCAlfredo Petrov Manager

There is a locality where tiny but complete Japan-law crosses are not rare: https://www.mindat.org/loc-259548.html

I don't recall ever seeing a half-twin of the 96 degree habit. Curious.

19th Dec 2018 22:31 UTCDana Morong

I wonder whether using the Ascii character of º 167 for the degreeº symbol will work in mindat (putting the number lock On and then typing 167 on the number keyboard at the same time that the Alt button is held down).º

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

It could be that the environment under which Japan Law Twins are encouraged to grow may favor one angle ove3r the other due to "handedness" or possibly "chirality" (which causes handedness). The difference between 84 degrees and 96 degrees is small when trying to estivate it by eyesight and could be overlooked. In particular when the individual quartz crystals are tapered by alternate growth of the rhombohedral and prismatic faces.

20th Dec 2018 20:30 UTCMichael Sommers

Part of the reason why I ask, is to my eye the synthetically re-grown crystal pictured above, I don't believe the "bottom half" is a twin. I see the left-side twin half growing over the right side half in the down-right direction and vice-versa (outlined), and I don't see a suture line for a twin on that half either (circled). So they just look like overgrowing crystals to me. Of course, I'm just looking at a photo.

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

Yes, it does seem like it. Looks like 2 twins tacked on to each other sometime during formation.

21st Dec 2018 17:57 UTCRonald J. Pellar Expert

The lack of 96 degree Japan Law Twins may be due to the "chiral" or "handedness of the quartz itself. In a true twin, the twin plane is a plane throught the crystal structure that is the same for both twin crystals. The spiral nature of the atomic arrangement within a chiral crystal may be restricted to the 84 degree direction. Meshing spirals at an angle requires a rather exact atomic arrangement on the twin plane. Therefor, the 96 degree angle twin plane my not be possible. That could explain the fact that the small quartz crystal that forms the 96 º 27' angle with the left twin crystal in my previous photo looks smaller and does not appear to be a attached to the left twin crystal. Thus this 96º crystal is simply an extention of the right twin crystal. This would also explain the Japan Law Twin "crosses" also shown above by Michael. This would also explain the total lack of 96º Japan Law Twin pairs in general.

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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