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Long-range and short-range cation order in the crystal structures of carlfrancisite and mcgovernite

Published online by Cambridge University Press:  15 May 2018

Frank C. Hawthorne
Frank C. Hawthorne*
Affiliation:
Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
*
E-mail: [email protected]
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Abstract

The crystal structures of carlfrancisite, ideally Mn32+(Mn2+,Mg,Fe3+,Al)42(As3+O3)2(As5+O4)4[(Si,As5+)O4]8(OH)42, hexagonal (rhombohedral), R3̄m with Z = 6, and unit-cell parameters: a = 8.2238(2), c = 205.113(6) Å and V = 12013.5(4) Å3, from the Kombat mine, Otavi Valley, Namibia, and mcgovernite, ideally Zn3(Mn2+,Mg,Fe3+,Al)42(As3+O3)2(As5+O4)4[(Si,As5+)O4]8(OH)42, hexagonal (rhombohedral), R3̄m with Z = 6, and unit-cell parameters: a = 8.2061(3), c = 204.118(8) Å and V = 11903.8(6) Å3, from Sterling Hill, New Jersey, have been solved by direct methods and refined to R1 values of 3.37 and 5.02% for 3837 and 3772 unique observed reflections, respectively; they are isostructural. Chemical analysis by electron microprobe and crystal-structure refinement gave the following compositions: carlfrancisite: As2O5 12.89, As2O3 3.33, P2O5 0.50, V2O5 0.74, SiO2 8.96, Al2O3 0.78, FeO 0.22, MnO 53.25, MgO 9.37, H2O(calc) 8.42, sum 98.50 wt.%; mcgovernite: As2O5 13.06, As2O3 3.71, SiO2 9.34, Al2O3 0.20, FeO 1.38, MnO 44.58, ZnO 8.81, MgO 8.89, H2O(calc) 8.24, sum 98.21 wt.%. The H2O contents and the valence states of As were determined by crystal-structure analysis.

There are 18 crystallographically distinct cation sites in both carlfrancisite and mcgovernite. There are two [4]-coordinated As sites fully occupied by As5+, and four T sites occupied by Si and As5+ in solid solution. The As(3) site has triangular pyramidal coordination with <As(3)–O> distances of 1.808 and 1.817 Å, typical of As3+. The Z(1) site, occupied by Mn2+ in carlfrancisite and Zn in mcgovernite, has tetrahedral coordination, and the Z(2) site is only partly occupied by Mg and Mn2+ in both structures. There are nine M sites, all of which are octahedrally coordinated and contain dominantly Mn2+ and Mg, with minor Al and Fe. There are three cation sites with significant vacancies: As(3), Z(2), M(3), and there are complicated patterns of short-range order involving the cations and vacancies at these sites.

The carlfrancisite–mcgovernite structure contains 84 layers of approximately close-packed polyhedra along one translation on c. The anions in the structure are arranged in approximately close-packed layers orthogonal to the c axis. Fourteen layers stack along the c axis in the sequence |**hhchch•hchchh| (* denotes a layer of anions displaced from close packed). There are eight distinct layers of cation-centred polyhedra that repeat via a centre of symmetry at the origin, and via the R-centering to give 84 layers per unit-cell.

Keywords

mcgovernitecarlfrancisitecrystal structurearsenateelectron-microprobe analysis
Type
Article
Information
Mineralogical Magazine , Volume 82 , Issue 5 , October 2018 , pp. 1101 - 1118
Copyright
Copyright © Mineralogical Society of Great Britain and Ireland 2018 

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Footnotes

Associate Editor: G. Diego Gatta

References

Araki, T. and Moore, P.B. (1981) Dixenite, Cu1+Mn2+14Fe3+(OH)6(As3+O3)5(Si4+O4)5(As5+O4): metallic [As43+Cu1+] clusters in an oxide matrix. American Mineralogist, 66, 1263–1273.Google Scholar
Brown, I.D. (2002) The Chemical Bond in Inorganic Chemistry. The Bond Valence Model. Oxford University Press, Oxford, UK.Google Scholar
Brown, I.D. (2016) The Chemical Bond in Inorganic Chemistry. The Bond Valence Model. 2nd edition. Oxford University Press, Oxford, UK.Google Scholar
Brugger, J., Armbruster, T., Meisser, N., Hejny, C. and Grobety, B. (2001) Description and crystal structure of turtmannite, a new mineral with a 68 Å period related to mcgovernite. American Mineralogist, 86, 1494–1505.Google Scholar
Bruker, (1997) SHELXTL Reference Manual 5.1., Bruker AXS Inc., Madison, WI, USA.Google Scholar
Cooper, M.A. and Hawthorne, F.C. (1999) The effect of differences in coordination on ordering of polyvalent cations in close-packed structures: the crystal structure of arakiite and comparison with hematolite. The Canadian Mineralogist, 37, 1471–1482.Google Scholar
Cooper, M.A. and Hawthorne, F.C. (2001) The biggest mineral: The crystal structure of mcgovernite. Eleventh Annual V.M. Goldschmidt Conference, Abstract No. 3446. Available at https://www.lpi.usra.edu/meetings/gold2001/pdf/3446.pdfGoogle Scholar
Cooper, M.A. and Hawthorne, F.C. (2012) The crystal structure of kraisslite, [4]Zn3(Mn,Mg)25(Fe3+,Al)(As3+O3)2[(Si,As5+)O4]10(OH)16, from the Sterling Hill mine, Ogdensburg, Sussex County, New Jersey, USA. Mineralogical Magazine, 76, 2819–2836.Google Scholar
Dunn, P.J., Peacor, D.R., Erd, R.C. and Ramik, R.A. (1986) Franciscanite and örebroite, two minerals from California and Sweden, related to redefined welinite. American Mineralogist, 71, 1522–1526.Google Scholar
Dunn, P.J., Francis, C.A. and Innes, J. (1988) A mcgovernite-like mineral and leucophoenicite from the Kombat mine, Namibia. American Mineralogist, 73, 1182–1185.Google Scholar
Gagné, O. and Hawthorne, F.C. (2015) Comprehensive derivation of bond-valence parameters for ion pairs involving oxygen. Acta Crystallographica, B71, 562–578.Google Scholar
Hawthorne, F.C. (1983) Quantitative characterization of site occupancies in minerals. American Mineralogist, 68, 287–306.Google Scholar
Hawthorne, F.C. (1996) Structural mechanisms for light-element variations in tourmaline. Canadian Mineralogist, 34, 123–132.Google Scholar
Hawthorne, F.C. (1997) Short-range order in amphiboles: a bond-valence approach. Canadian Mineralogist, 35, 203–218.Google Scholar
Hawthorne, F.C. (2016) Short-range atomic arrangements in minerals. I: The minerals of the amphibole, tourmaline and pyroxene supergroups. European Journal of Mineralogy, 28, 513–536.Google Scholar
Hawthorne, F.C., Ungaretti, L., Oberti, R., Caucia, F. and Callegari, A. (1993) The crystal chemistry of staurolite. III. Local order and chemical composition. The Canadian Mineralogist, 31, 597–616.Google Scholar
Hawthorne, F.C., Ungaretti, L. and Oberti, R. (1995) Site populations in minerals: terminology and presentation of results of crystal-structure refinement. The Canadian Mineralogist, 33, 907–911.Google Scholar
Hawthorne, F.C., Della Ventura, G. and Robert, J.-L. (1996) Short-range order of (Na,K) and Al in tremolite: An infrared study. American Mineralogist, 81, 782–784.Google Scholar
Hawthorne, F.C., Abdu, Y.A., Ball, N.A. and Pinch, W.W. (2013) Carlfrancisite: Mn32+(Mn2+,Mg,Fe3+,Al)42[As3+O3]2(As5+O4)4[(Si,As5+)O4]6 [(As5+,si)O4]2 (OH)42, a new arseno-silicate mineral from the Kombat mine, Otavi valley, Namibia. American Mineralogist, 98, 1693–1696.Google Scholar
Lafuente, B., Downs, R.T., Yang, H. and Stone, N. (2015) The power of databases: the RRUFF project. Pp 1–30 in: Highlights in Mineralogical Crystallography (Armbruster, T. and Danisi, R.M., editors). De Gruyter, Berlin, Germany.Google Scholar
Majzlan, J., Drahota, P. and Filippi, M. (2014) Paragenesis and crystal chemistry of arsenic minerals. Pp. 17–184 in: Arsenic: Environmental Geochemistry, Mineralogy, and Microbiology (Bowell, R.J., Alpers, C.N., Jamieson, H.E., Nordstrom, D.K. and Majzlan, J., editors) Reviews in Mineralogy and Geochemistry, 79. Mineralogical Society of America and the Geochemical Society, Chantilly, Virginia, USA.Google Scholar
Moore, P.B. (1967) The crystal structure of welinite, (Mn+4,W)<1(Mn+2,W,Mg)<3Si(O,OH)7. Arkiv för mineralogi och geologi, 24, 459–466.Google Scholar
Moore, P.B. and Araki, T. (1978) Hematolite: a complex dense-packed sheet structure. American Mineralogist, 63, 150–159.Google Scholar
Moore, P.B. and Ito, J. (1978) Kraisslite, a new platy arsenosilicate from Sterling Hill, New Jersey. American Mineralogist, 63, 938–940.Google Scholar
Palache, C. and Bauer, L.H. (1927) Mcgovernite, a new mineral from Sterling Hill, New Jersey. American Mineralogist, 12, 373–374.Google Scholar
Pertlik, F. (1986) The crystal structure of franciscanite, Mn3(Vx□1–x)(SiO4)(O,OH)3, [x = 0.5]. Neues Jahrbuch für Mineralogie, Monathefte, 1986, 493–499.Google Scholar
Pouchou, J.L. and Pichoir, F. (1985) ‘PAP’ (φρZ) procedure for improved quantitative microanalysis. Pp. 104–106 in: Microbeam Analysis (Armstrong, J.T., editor). San Francisco Press, San Francisco, California, USA.Google Scholar
Sheldrick, G.M. (2008) A short history of SHELX. Acta Crystallographica, A64, 112–122.Google Scholar
Wuensch, B.J. (1960) The crystallography of mcgovernite, a complex arsenosilicate. American Mineralogist, 45, 937–945.Google Scholar
Wuensch, B.J. (1968) Comparison of the crystallography of dixenite, mcgovernite and hematolite. Zeitschrift für Kristallographie, 127, 309–318.Google Scholar
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