FMF - Friends of Minerals Forum, discussion and message board

[Jordi Fabre]

We have an interesting discussion in the Spanish forum about twinned minerals ( https://www.foro-minerales.com/forum/viewtopic.php?t=2330 ) and we have a doubt about a possible twined Quartz.

I can't see there a twin, but two crystals growing together (specially due the fact that one seems to have a doubly termination ending upper the first crystal) but other Spanish minsurfers have a different opinion and they say that it is a Japan law twin.

Can you help please?

Jordi

[garchin]

with Japanese Law there should only be contact not penetration

[parfaitelumiere]

is it possible to have a photo where we see a reflect on the common face of the both crystals?
We often see flat crystals,and never see steps on the flat common face of the two "crystals" of the twin.
It's not easy to see if twinned on a photo!

[parfaitelumiere]

after seeing at the spanish version,I think it's not twinned,the 84'34" is not present here,it seems to be more than 90'

[chris]

Hi Jordi,

I agree with Parfaitelumiere, the angle is to open to be a law twin. Moreover on the second picture it seems the crystals edges don't match one another properly to be a twin. Maybe a larger picture would help.

Christophe

[alfredo]

Measure the angle; it's a bit less than 90 degrees!

[Pete Richards]

I think this is likely to be a Japan law twin. The best way to measure the angle would be to measure the angles between striations on the prism faces of both individuals, if they are well-developed.

The fact that both crystals are distorted (flattened) argues for the twin; this typically does not happen with chance intergrowths. The two individuals are basically in contact; there may be a little overgrowth of one individual into the "space" of the other, but this often happens in contact twins of other minerals such as calcite, and could happen with quartz, particularly if the supply of new ions is from one direction, to one side of the crystal group.

I think we often idealize our expectations for twins and crystal habits in general. This is not an ideal Japan law twin, but I think it is one none the less....

[garchin]

wow Pete, very well said. I think I agree with you! Too often striving for perfection
has narrowed our perception of other possibilities. But one more thing. Some mineral sellers donot include pictures. When a dealer is selling this specimen as Japan Law for a substantial amount I donot think I will be very happy opening the package.

[parfaitelumiere]

It's exact that crystals are flatened,maybe one is a little bit distored,and has grown a little bit on the other,maybe it has broken,or partially broken,and grown a second time,a little bit like gwindel do,the second generation,half open crystals after sugar crystals.
the best would be to measure the angle between striations,of course.

[John S. White]

I tend to agree with Pete that this likely is a Japan law twin, but a better photo would help. Further, I think you might find that the angle between the two members of this "twin" is the complement of the normal angle of 84°33', in other words 95°27', which is perfectly okay. In the photo the internal angle does appear to be greater than 90°. I disagree with garchin, examples of Japan law twins exhibiting penetration are indeed known.

[Jordi Fabre]

A new photo of the same specimen.