[sdpd] Re: Minerals with unknown structure (>300)

[alb...@cristal.org]

> A starting list of > 300
> minerals with apparently unknown structure is available at :
> http://www.cristal.org/iniref/sdpd-minerals.html

In order to avoid simultaneous efforts, that list
will be updated with some results.

First try : nepouite Ni3Si2O5(OH)4, 
ICDD entries : 15-0580, 20-0791, 25-0524
Well, if you see the search-match result available
at the above web page, you will see that very probably,
another mineral with a different name (pecoraite), but 
same chemical formula is possibly the same material.
Pecoraite corresponds to the ICDD recent entry 49-1859, data
from a publication in Clay Miner., 1995, and indexing  
in monoclinic from 6 diffraction lines and a figure of
merit F(6) = 1 (0.102, 118), wow ! Robin, don't laugh ! 

Anyway, a structure determination of nepouite/pecoraite
from powder diffraction data appears an impossible mission,
you may get the pattern at the above web site too.

My conclusion is that increasing the ICDD database content 
with redundant bad data is continuing.

The studied nepouite sample sample appears to contain a bit 
of willemseite, (Ni,Mg)3Si4O10(OH)2, apparently with unknown 
structure too (nothing in ICSD), and F(30)= 2 (0.037, 496)
in the 22-0711 ICDD entry (re-wow !).

Armel Le bail
http://www.cristal.org/course/


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