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Recovering - Academic
Joined: 24 Apr 2018
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 Posted: Nov 09, 2018 18:12 Post subject: Re: Rarest quartz twins with inclined axes C |
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| John S. White wrote: | | It may seem a small point but the proper name for the twin is Japan law twin, not Japanese twin. Japanese twins are properly represented in the attached image. |
REAL JAPAN LAW TWINS
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Recovering - Academic
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| Posted: Nov 09, 2018 18:16 Post subject: Re: Rarest quartz twins with inclined axes C |
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Interesting!!
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Recovering - Academic
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Posts: 316
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| Posted: Nov 09, 2018 18:17 Post subject: Re: Rarest quartz twins with inclined axes C |
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| Bob Morgan wrote: | At the risk of adding confusion to this discussion, I prefer to call what Pete calls auto-epitaxy deposition twins. This is where a smaller crystal develops on an already established larger crystal and does so according to the twin law showing the same characteristic morphology of 'v' twins. This is quite common with Japan Law twinning. It is true of quite a lot of Greiserntal Law twins. In both cases there is more rapid growth in the twin notch, rapid widening of the smaller crystal, and markedly less growth in the supplemental angle on the other side of the smaller crystal. If the larger crystal is clear, the twin composition plane shows and is consistent with the twin law.
These depositions can be oriented in either of two directions 1) with the twin angle toward the termination of the larger crystal or 2) with the twin angle toward the base of the larger crystal. There are several instances where a larger crystal hosts separate twins of both orientations.
Now, this leads me to comment on the supposedly Reichenstein Law. There is no rational twin plane or twin axis for such a law. The photo's showing parallel pyramidal faces are therefore just the supplementary angle to the Greiseerntal Law twin that is oriented toward the larger crystal's base. Note too, that Japam Law twins have two sets of parallel pyramidal faces across the supplementary 96 degree angle, and that's not a separate twin law. |
Interesting!!!
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