In the series of dark database stories, below is a new one.
Trying (this week) to identify a mineralogical sample,
I had a clearly positive match with the 26-1011, 41-1382
and 42-1427 JCPDS-ICDD cards,
Formula Al(SO4)(OH,F).5H2O, rostite, or khademite (if F
only). Note that the 41-1382 is said to replace the 42-1427,
telling us that the ICDD sets are not made incrementally, or
that preparing a new set, the ICDD people tolerate the entry
of several new cards describing the same compound, well
whatever this is telling us !-).
Anyway, I am interested in unknown structures. And since
the inclusion of ICSD calculated powder pattern into ICSD,
theoretically, if an inorganic/mineral compound shows only
a match with a card starting by <70, then there could be
3 main explanations :
1- the ICDD card merit to be deleted,
2- the structure is unknown,
3- the ICSD is uncomplete.
(these main 3 explanations because the ICDD never says
if the crystal structure is known...).
Well, in that case, it is the last explanation which applies...
But how to demonstrate this ? I visited many mineralogical
databases, for instance :
http://www.webmineral.com/
http://www.webmineral.com/data/Khademite.shtml
and finally found the structure and reference in a Russian
database (Institute of Experimental Mineralogy - Russian
Academy of Sciences), activating the hyperlink in the
Webmineral one :
http://database.iem.ac.ru/mincryst/s_carta.php3?KHADEMITE
the coordinates are in the full information card :
http://database.iem.ac.ru/mincryst/s_carta.php3?KHADEMITE
For the ICSD bibliographists, *if I am not wrong in that story*, they
should consult this reference :
Bachet B., Cesbron F., Chevalier R. (1981). Bull. Mineral., 104, 19-22.
(this new ICSD entry will add automatically a new ICDD card...)
Thanks to these many mineral databases available for free on
the Internet !! Think to them !
Best regards,
Armel Le Bail
http://sdpd.univ-lemans.fr/course/
