Dear all, We all know minerals can form twins. Polysynthetic twins (= all the composition surfaces are parallel) can have an infinite number of individal crystals that are twinned with each other. Considering the non-polysynthethic twins (here defined as a twin where some composition surfaces can be parallel, but not all the composition surfaces are parallel) , the number of individual crystals that can make up a twin is much more limited. Of course two crystals is the lower limit. But what is *the maximum number of crystals ever counted in a non-polysynthethic twin (as defined above)*? And what was/is the mineral species? I have a candidate (the mineral name starts with a "p"), but I would like to be certain ... Cheers, Herwig

Dear Herwig, Polysynthetic twins are, of course, abundant in minerals belonging to the plagioclase solid solution ("plagioclase" is not a mineral name, but a name given to designate members of the albite-anorthite series). But under the polarizing microscope, tiny polysynthetic twins (in two directions) are also observed in microcline, as well as in leucite. Due to the very small thickness of the lamellae constituting these twins, I think that they are certainly more numerous than the crystals involved in the plagioclase twins. Maybe someone more specialized in the investigation of feldspars by HRTEM would give a more accurate answer. Best wishes, Frédéric -------------------------------------------------- Professor Frédéric HATERT Laboratory of Mineralogy University of Liège B18 B-4000 Liège Belgium +32-4-366.21.43 fhatert@uliege.be https://www.minera.uliege.be/ -------------------------------------------------- ----- Mail original ----- De: "Herwig Pelckmans via MSA-talk" <msa-talk@minlists.org> À: msa-talk@minlists.org Envoyé: Mardi 16 Novembre 2021 11:11:26 Objet: [MSA-talk] Non-polysynthethic twins: highest number of individual crystals? Dear all, We all know minerals can form twins. Polysynthetic twins (= all the composition surfaces are parallel) can have an infinite number of individal crystals that are twinned with each other. Considering the non-polysynthethic twins (here defined as a twin where some composition surfaces can be parallel, but not all the composition surfaces are parallel) , the number of individual crystals that can make up a twin is much more limited. Of course two crystals is the lower limit. But what is the maximum number of crystals ever counted in a non-polysynthethic twin (as defined above) ? And what was/is the mineral species? I have a candidate (the mineral name starts with a "p"), but I would like to be certain ... Cheers, Herwig _______________________________________________ MSA-talk mailing list -- msa-talk@minlists.org To unsubscribe send an email to msa-talk-leave@minlists.org

Dear Frédéric, Thanks for your reply. I was thinking of macrocrystals (visible with the naked eye) rather than twinning observed through the POL. It seems answering my question is not as easy as I thought. More self study is needed, but that's always a good thing! Cheers, Herwig <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> Virusvrij. www.avg.com <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> Op wo 17 nov. 2021 om 07:14 schreef <fhatert@uliege.be>: > Dear Herwig, > > Polysynthetic twins are, of course, abundant in minerals belonging to the > plagioclase solid solution ("plagioclase" is not a mineral name, but a name > given to designate members of the albite-anorthite series). > But under the polarizing microscope, tiny polysynthetic twins (in two > directions) are also observed in microcline, as well as in leucite. Due to > the very small thickness of the lamellae constituting these twins, I think > that they are certainly more numerous than the crystals involved in the > plagioclase twins. > Maybe someone more specialized in the investigation of feldspars by HRTEM > would give a more accurate answer. > Best wishes, > > Frédéric > > -------------------------------------------------- > Professor Frédéric HATERT > Laboratory of Mineralogy > University of Liège B18 > B-4000 Liège > Belgium > +32-4-366.21.43 > fhatert@uliege.be > https://www.minera.uliege.be/ > -------------------------------------------------- > > ----- Mail original ----- > De: "Herwig Pelckmans via MSA-talk" <msa-talk@minlists.org> > À: msa-talk@minlists.org > Envoyé: Mardi 16 Novembre 2021 11:11:26 > Objet: [MSA-talk] Non-polysynthethic twins: highest number of individual > crystals? > > Dear all, > We all know minerals can form twins. > Polysynthetic twins (= all the composition surfaces are parallel) can have > an infinite number of individal crystals that are twinned with each other. > Considering the non-polysynthethic twins (here defined as a twin where > some composition surfaces can be parallel, but not all the composition > surfaces are parallel) , the number of individual crystals that can make up > a twin is much more limited. > Of course two crystals is the lower limit. > But what is the maximum number of crystals ever counted in a > non-polysynthethic twin (as defined above) ? And what was/is the mineral > species? > > I have a candidate (the mineral name starts with a "p"), but I would like > to be certain ... > Cheers, Herwig > > _______________________________________________ > MSA-talk mailing list -- msa-talk@minlists.org > To unsubscribe send an email to msa-talk-leave@minlists.org >