It seems to me that it is legitimate to refer to what you describe as "twinning". That's the difference between merohedral and non-merohedral twinning. What you describe is non-merohedral twinning. In fact twinning has been (re)discovered by most of the biological community after the remarkable article by T.O. Yeates in Methods in Enz. (1997) vol 276A pp. 344-358. Only after this reminder did papers in biocrystallography mention twinning currently. (I can refer to my own experience because the Yeates' paper allowed us (1) to discover the problem of twinning and (2) to solve a twinned structure). Probably, your feeling comes from the fact that structural biologists were only concerned by solving their structure and never considered multiple crystals (non-merohedral twinning) as a real problem, but only as a practical problem, since everyone knew that such crystals had to be either let aside or broken into single crystals. However, twinning has always been extremely well know in mineralogy because it is extremely common to see natural crystals showing non-merohedral twinning. And mineralogists commonly have long described crystal habits by twinning observed with crystals of specific molecules.
I suggest that you ask google for "macle rutile wurtzite quartz" (macle is twinning in French) and you select images. All these photographs are for twinned crystals. All of that was extremely well described in a venerable book by Friedel in 1911 when none of us was born. I think all of that is not just pure semantics. Am I wrong ? Philippe Dumas De: "Ana Luísa Moreira de Carvalho" <[email protected]> À: "CCP4BB" <[email protected]> Envoyé: Mercredi 17 Mars 2021 11:12:53 Objet: Re: [ccp4bb] Can twinning be seen in the diffraction pattern? Just a short note on this: I often see colleagues using the word “twinning" when referring to a crystal that is actually multiple (not single). I think much confusion arises from this. For me, a twin crystal is the one that looks single under the microscope and only intensity statistics reveal that the diffraction comes from more than one crystal. If a crystal looks multiple, i do not call it a twin. Am i being too meticulous on this? Thanks! On 16 Mar 2021, at 13:31, Eleanor Dodson < [ mailto:[email protected] | [email protected] ] > wrote: You usually detect twinning most reliably from the intensity statistics - CCP4I2 and Xtriage report those.. Eleanor On Tue, 16 Mar 2021 at 07:31, Marina Gárdonyi < [ mailto:[email protected] | [email protected] ] > wrote: BQ_BEGIN Dear all, thanks to all who helped me solving the question. You sent me a lot of comments and information I have not taken into account. After reading all the answers, I have come to the conclusion that the spots that are very close to each other come from the long cell axis (57-57-160) and that twinning can probably not be seen in my case. I should have mentioned that the diffraction images came from an in-house x-ray machine, recorded with a 0.5 degree rotation range. Thank you all again! Kind regards, Marina -- Marina Gárdonyi PhD Student, Research Group Professor Dr. Klebe Department of Pharmaceutical Chemistry Philipps-University Marburg Marbacher Weg 6, 35032 Marburg, Germany Phone: +49 6421 28 21392 E-Mail: [ mailto:[email protected] | [email protected] ] [ http://www.agklebe.de/ | http://www.agklebe.de/ ] ######################################################################## To unsubscribe from the CCP4BB list, click the following link: [ https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 | https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 ] This message was issued to members of [ http://www.jiscmail.ac.uk/CCP4BB | www.jiscmail.ac.uk/CCP4BB ] , a mailing list hosted by [ http://www.jiscmail.ac.uk/ | www.jiscmail.ac.uk ] , terms & conditions are available at [ https://www.jiscmail.ac.uk/policyandsecurity/ | https://www.jiscmail.ac.uk/policyandsecurity/ ] To unsubscribe from the CCP4BB list, click the following link: [ https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 | https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 ] BQ_END To unsubscribe from the CCP4BB list, click the following link: [ https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 | https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 ] ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 This message was issued to members of www.jiscmail.ac.uk/CCP4BB, a mailing list hosted by www.jiscmail.ac.uk, terms & conditions are available at https://www.jiscmail.ac.uk/policyandsecurity/
