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GEOREF RECORD

The crystal structure of stichtite, re-examination of barbertonite, and the nature of polytypism in MgCr hydrotalcites

Stuart J. Mills, Pamela S. Whitfield, Siobhan A. Wilson, Joanne N. Woodhouse, Gregory M. Dipple, Mati Raudsepp and Carl A. Francis
The crystal structure of stichtite, re-examination of barbertonite, and the nature of polytypism in MgCr hydrotalcites
American Mineralogist (January 2011) 96 (1): 179-187

Abstract

Stichtite, ideally Mg (sub 6) Cr (sub 2) CO (sub 3) (OH) (sub 16) .4H (sub 2) O, from Stichtite Hill, Tasmania, Australia, and barbertonite, also ideally Mg (sub 6) Cr (sub 2) CO (sub 3) (OH) (sub 16) .4H (sub 2) O, from the Kaapsehoop asbestos mine, South Africa, have been studied by powder X-ray diffraction and their structures have been refined using the Rietveld method. Stichtite from Stichtite Hill crystallizes in the rhombohedral space group R3m, with unit-cell parameters a=3.09575(3) and c=23.5069(6) Aa, V=195.099(6) Aa (super 3) , with Z=3/8. Barbertonite from the Kaapsehoop asbestos mine crystallizes in the hexagonal space group P6 (sub 3) /mmc. The co-type specimens of barbertonite were found to be intergrown mixtures consisting of barbertonite and stichtite. Unit-cell parameters of barbertonite from the co-type specimens were a=3.09689(6), c=15.6193(8) Aa, and V=129.731(8) Aa (super 3) and a=3.09646(6), c=15.627(1) Aa V=129.76(1) Aa (super 3) , and Z=1/4. Rietveld refinements of both stichtite and barbertonite show that they are polytypes rather than polymorphs and do not represent distinct mineral species. Several possible nomenclature systems are discussed for the naming of hydrotalcite minerals and groups. Raman band assignments are also presented for stichtite from Stichtite Hill. Stichtite and hydrotalcite minerals make up a large proportion of the ore at the Mount Keith nickel mine in Western Australia. Bulk powder diffraction shows the ore contains 6.1 wt% stichtite and 5.6 wt% iowaite. Hydrotalcite group minerals provide an important potential reservoir of CO (sub 2) . At Mount Keith, the amount of CO (sub 2) mined as stichtite could exceed 45 000 metric tons per year, while exchange of Cl for CO (sub 3) could fix in excess of 40 000 metric tons CO (sub 2) per year if end-member iowaite is reacted to form pyaroaurite.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 96
Serial Issue: 1
Title: The crystal structure of stichtite, re-examination of barbertonite, and the nature of polytypism in MgCr hydrotalcites
Affiliation: University of British Columbia, Mineral Deposit Research Unit, Vancouver, BC, Canada
Pages: 179-187
Published: 201101
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 54
Accession Number: 2011-012701
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables
S43°40'00" - S39°30'00", E143°49'60" - E148°30'00"
S35°00'00" - S22°00'00", E16°00'00" - E33°00'00"
Secondary Affiliation: NRC Canada, Institute for Chemical Process and Environmental Technology, CAN, CanadaHarvard Mineralogical Museum, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201108
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