FMF - Friends of Minerals Forum, discussion and message board

[Reef]

One of the most favorite types of twinning
Disentis law twin

[Pete Richards]

Reef, thanks for your comments. Your drawings are quite useful - you are right that (as far as I know) these rare relationships for quartz have been described verbally only. Can you tell us how you made the diagrams?

Your suggestion that Frondel's doubts about these rare relationships stems from their scarcity is undoubtedly true (but perhaps not the whole story). And having images to look at may lead to more discoveries. However, for true twinning the lattice rules the orientation, and deviation from the theoretical angular relationship of more than a fragment of a degree is enough to call into question the validity of a proposed example, in contrast to its being a random orientation. Precise measurement is critical in building a convincing case.

I would encourage you to look up the recent treatment of twinning in general that Josele cited. It is excellent and rigorous, and I was not aware of it (thanks, Josele). As I read it, your rare relationships would not count as true twins according to this treatment, but would probably be considered pleisiotwins, for which the relationship requirements are much looser.

Finally, I think you misunderstood what I meant by "classical twinning". The Brazil and Dauphine twins are penetration twins and conform to classical concepts. But the Japan law twin also conforms to classical concepts (of contact twinning) in the sense that it involves two equal individuals related across a crystallographic plane with low Miller indices. To these examples of classical twins, I think we can add the Reichenstein twin and the Grieserntal twin, which have been found with some frequency in the northwestern US, and the so-called Belovda twin (by contact on (302) ), for which two absolutely convincing large specimens from different localities are known.

These are all examples of twins in the classical sense, the first two being penetration twins and the others being contact twins

[Reef]

Pete, thanks for the corrections. About the schematic drawings, a little prehistory. Two years ago I became interested in quartz twins. According to the book K. Frondel at first absolutely did not understand anything. I began to study all available literature on this topic. I tried to glue crystals together in some twin positions for visualization. Gradually came the understanding of how they look. It turned out that in this book all elementary simply it is written. Plus to knowledge, began to find twins on one small manifestation of quartz.Picture will certainly help to find the supposed twins, but the proof will of course be the measurement of angles or X-ray analysis. But some twins (for example disentis, Japanese) can be determined with great certainty visually by the glare of the corresponding faces.I do not know to which subtype of twinning all these laws apply. These subtleties are of interest to a very narrow circle of specialists, but not for amateurs. I know the historical names and add new labels, I think it's wrong. You will not deny that they exist, regardless of the name.
As for the Japanese twins, I will prepare and discuss some issues.

[Reef]

The concept of two equal individuals in twins is wrong.
In the laws of twinning, there is no condition for the relative dimensions of subindivids.
Here are some examples.
Japan Law Twin

[Jordi Fabre]

Hi Reef,

Please use the pull-down list when you add images. Up to know we are doing it for you but is a lot of work for us.

To know how it works please use: New Data Base of localities within the FMF!

[Reef]

Hi Jordi. Thank you. Overlooked.

Another variant of the arrangement is in the twins of the Japanese type.
There was a splicing of prisms. A small crystal is located on the prism of a large crystal and partially submerged. The angle and parallelism of the faces correspond to the Japanese twinning law. Up to X - shape does not grow, absorption will take place. Maybe I missed something? Is this a Japanese twin ?

[Reef]

Can anyone confirm or disprove this opinion (previous message)? If such splices (a prism to a prism) do not contradict the laws of twinning, then the circle of search for twins will expand. And we can wait for new finds. This applies only to the analogues of the Japanese twins.

For a more in-depth study on this topic, I recommend reading Hans Grimmer "Quartz aggregates revisited"

[John S. White]

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.

[Jordi Fabre]

[Reef]

I agree, pleasant twins.
The costs of machine translation. The main thing is for people to understand what the conversation is about.

Continue..
Goldschmidt law twin
Angle 47°43'

[Reef]

Breithaupt law twin
Angle 48°54'

[Reef]

Zwickau law twin
Angle 42°17'

[Reef]

Friedel Law Twin
Angle 90°

[Josele]

Reef, thank you for sharing your schemes of these little known twins. Is a hard work to recognize them in practice because the need of very accurate measurements. My level in crystallography does not allow me to enter into a scientific discussion, but it is interesting to know that they exist. Henceforth I will look at quartz aggregates carefully and with more interest.

[Reef]

Josele, good luck with your search !

Reichenstein - Griesernthal law twin