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Mineralogical ClassificationRedefinition of zdenekite crystallography

28th Nov 2003 13:05 UTCUwe

Zdenekite, originally described as tetragonal, has

space group P21/n, a = 10.023(7), b = 19.55(1), c = 10.023(6) A, beta =90.02(1)°, Z = 4.

The structure is closely related to that of lavendulan (P21/n), sampleite (P21/n) and the P21/c-polymorph of sampleite (paper in prep.).



Ref.

N. V. Zubkova, D. Yu. Pushcharovsky, H. Sarp, S. J. Teat, and E. J. MacLean (2003): Crystal structure of zdenekite NaPbCu5(AsO4)4Cl.5H2O. Crystallography Reports, 48, 939-943.

28th Nov 2003 14:15 UTCMarco Ciriotti

Thank you Uwe.

So the orthorhombicity of lavendulan and sampleite is not correct.

And in the lavendulan group they are two "subgroup unit" : monoclinic (lavendulan, sampleite, P21/c polymorph of sampleite, with Z = 4) and tetragonal (mahnertite and lemanskite, with Z = 8).



Shubnikovite (space group unknown) may be a related phase?

28th Nov 2003 14:35 UTCUwe

In my opinion, shubnikovite is so poorly characterised (for instance, no X-ray powder diffraction pattern exists!) that it may well need to be discredited (but definitely reinvestigated). Crystal data published suggest it could be lavendulan, but with a wrong orientation of the crystal axes.



The status of this species is critically discussed in our to-be-submitted paper on lavendulan etc.



Cheers, Uwe

28th Nov 2003 15:01 UTCMarco Ciriotti

I forgot zdenekite in the monoclinic subgroup! but it is clear...that must be added.
 
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