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Arsenohopeite; a new zinc arsenate mineral from the Tsumeb Mine, Namibia

F. Neuhold, U. Kolitsch, H. J. Bernhardt and C. L. Lengauer
Arsenohopeite; a new zinc arsenate mineral from the Tsumeb Mine, Namibia
Mineralogical Magazine (June 2012) 76 (3): 603-612


Arsenohopeite, ideally Zn (sub 3) (AsO (sub 4) ) (sub 2) .4H (sub 2) O, is the arsenate analogue of hopeite, Zn (sub 3) (PO (sub 4) ) (sub 2) .4H (sub 2) O (it is isostructural with alpha -hopeite). It was found as a single colourless to blue crystalline grain from the Tsumeb mine, Namibia. The holotype specimen is approximately 1X1X1 mm in size. Arsenohopeite is associated with tiny white fibres of an unidentified Zn- and As-bearing phase. It is orthorhombic, space group Pnma, with a = 10.804(2), b = 19.003(4), c = 5.112(1) Aa, V = 1049.5(4) Aa (super 3) and Z = 4. Electron microprobe analysis yielded: ZnO 44.92, Fe (sub 2) O (sub 3) 0.92, MnO 0.51, MgO 0.20, CuO 0.02, As (sub 2) O (sub 5) 45.84 (wt.%). The empirical formula is (Zn (sub 2.80) Fe (sub 0.06) Mn (sub 0.04) Mg (sub 0.03) ) (sub Sigma 2.93) (As (sub 1.01) O (sub 4) ) (sub 2) .4H (sub 2) O, based on 12 oxygen atoms. Optically, the mineral is biaxial negative, with alpha = 1.598(2), beta = 1.606(2), gamma = 1.613(2) (white light) and 2V (sub calc) = 86 degrees . It is not pleochroic or fluorescent. Arsenohopeite is translucent with a vitreous lustre. It is brittle, has an uneven fracture and (by analogy with hopeite) a cleavage that is perfect on {010}, good on {100} and poor on {001}. The calculated density is 3.420 g cm (super -3) . The five strongest calculated powder diffraction lines are [d in Aa (I)(hkl)]: 9.502 (100)(020), 2.926 (95)(241), 4.937 (50)(011), 4.110 (48)(230) and 3.567 (31)(240). The crystal structure of arsenohopeite has been solved by direct methods and refined in space group Pnma to R (sub 1) = 0.0353. Raman spectroscopy confirms the crystal-structure data and indicates the presence of weak hydrogen bonds.

ISSN: 0026-461X
EISSN: 1471-8022
Serial Title: Mineralogical Magazine
Serial Volume: 76
Serial Issue: 3
Title: Arsenohopeite; a new zinc arsenate mineral from the Tsumeb Mine, Namibia
Affiliation: Universitaet Wien, Institut fuer Mineralogie und Kristallographie, Vienna, Austria
Pages: 603-612
Published: 201206
Text Language: English
Publisher: Mineralogical Society, London, United Kingdom
References: 45
Accession Number: 2012-092171
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 7 tables
S19°13'00" - S19°13'00", E17°41'60" - E17°41'60"
Secondary Affiliation: Naturhistorisches Museum, AUT, AustriaRuhr-Universitaet Bochum, DEU, Germany
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201248
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