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Molybdophyllite: crystal structure, OD character, and relation to britvinite

Posted by Uwe Kolitsch  
Molybdophyllite: crystal structure, OD character, and relation to britvinite
May 11, 2012 01:03PM
    
U. Kolitsch, S. Merlino and D. Holtstam (2012): Molybdophyllite: crystal chemistry, crystal structure, OD character and modular relationships with britvinite. Mineral. Mag. 76, 493-516.

A detailed crystal-chemical study of the complex layered silicate molybdophyllite was conducted using
single-crystal X-ray diffraction (XRD) methods, supplemented by powder XRD, infrared (IR) and
Raman spectroscopic studies, chemical analyses by energy-dispersive spectrometry (EDS) on a
scanning electron microscope (SEM), and electron probe microanalysis (EPMA). The results, based on
several samples from both Långban and Harstigen, Filipstad, Sweden, show that the crystal structure of
molybdophyllite has an order-disorder (OD) character. The latter is especially evident in specimens
from Långban which display a complex diffraction pattern characterized by the simultaneous presence
of sharp spots, diffuse reflections and continuous streaks. The sharp reflections define the unit cell of
the family structure (a = 3.124, c = 41.832 Å, space group R32). Two main polytypes (maximum
degree of order structures) are indicated by the OD approach: a trigonal one and a monoclinic one; the
latter polytype is the most common in the samples that were studied and has space group C2, with a =
16.232(6), b = 9.373(2), c = 14.060(3) Å, b = 97.36(4)º and V = 2121.5(10) Å3.
The crystal structure determination [R1 = 0.096], together with the EPMA, IR and Raman data,
reveal that molybdophyllite is built up by a regular alternation of complex layers with a composition
{Mg9[Si10O28(OH)8][OPb4]2}6+ and simple layers with a composition [(CO3)3·H2O]6-, leading to the
ideal crystal-chemical formula Pb8Mg9[Si10O28(OH)8|O2|(CO3)3]·H2O (Z = 2).
This contribution is mainly devoted to the results obtained for molybdophyllite sensu stricto, but
new data for britvinite [i.e. ‘molybdophyllite-18 Å’] are also presented and its modular relationship
with molybdophyllite is discussed.



PDF available for interested people. Send PM or reply here.
Re: Molybdophyllite: crystal structure, OD character, and relation to britvinite
May 11, 2012 03:09PM
    
Interesting! Pls send an .pdf
Harald F.
Hello,

I know it's totally off-subject, but I was expecting some Mo in the formula, instead of lead, going by the name. I was thinking PLUMBOphyllite maybe...silly me. Talk about naming issues. BTW, being a native NJian, I still prefer Hancockite.

Back to subject...TTFN.


To absent friends...in memory...still bright.
Re: Molybdophyllite: crystal structure, OD character, and relation to britvinite
May 11, 2012 05:05PM
    
Harald: sent.
Steven: "molybdos" (Greek) means lead. The mineral was named in 1901 when naming minerals using Greek words was much more common than today.
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