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Mineralogical ClassificationMolybdophyllite: crystal structure, OD character, and relation to britvinite

11th May 2012 14:03 UTCUwe Kolitsch Manager

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 , together with the EPMA, IR and Raman data,

reveal that molybdophyllite is built up by a regular alternation of complex layers with a composition

{Mg92}6+ and simple layers with a composition <(CO3)3·H2O>6-, leading to the

ideal crystal-chemical formula Pb8Mg9·H2O (Z = 2).

This contribution is mainly devoted to the results obtained for molybdophyllite sensu stricto, but

new data for britvinite are also presented and its modular relationship

with molybdophyllite is discussed.

PDF available for interested people. Send PM or reply here.

11th May 2012 16:09 UTCHarald Oskar Folvik

Interesting! Pls send an .pdf

Harald F.

11th May 2012 17:13 UTCSteven Kittleson

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.

11th May 2012 18:05 UTCUwe Kolitsch Manager

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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