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Naalasite, NaAl(AsO3OH)2⋅H2O, the Al analogue of nafeasite from the Torrecillas mine, Iquique Province, Chile

Published online by Cambridge University Press:  22 January 2024

Anthony R. Kampf Open the ORCID record for Anthony R. Kampf [Opens in a new window] ,
Gerhard Möhn ,
Chi Ma Open the ORCID record for Chi Ma [Opens in a new window]  and
Joy Désor
Anthony R. Kampf*
Affiliation:
Mineral Sciences Department, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA
Gerhard Möhn
Affiliation:
Independent Researcher, Dr.-J.-Wittemannstrasse 5, 65527 Niedernhausen, Germany
Chi Ma
Affiliation:
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA
Joy Désor
Affiliation:
Independent Researcher, Bad Homburg, Germany
*
Corresponding author: Anthony R. Kampf; Email: akampf@nhm.org
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Abstract

The new mineral naalasite (IMA2023–027), NaAl(AsO3OH)2⋅H2O, was found at the Torrecillas mine, Iquique Province, Chile, where it is a secondary alteration phase associated with anhydrite, juansilvaite, magnesiokoritnigite and a lavendulan-like phase. Naalasite occurs in tightly intergrown aggregates and druses of equant crystals. Crystals are light to medium pink and transparent, with vitreous lustre and white streak. The Mohs hardness is ~3½. The density is 3.19(2) g⋅cm–3. Optically, naalasite is uniaxial (+), with ω = 1.630(3) and ɛ = 1.660(3) (white light). The empirical formula (based on 9 O apfu) is Na0.92Al0.61Fe3+0.39As2O9H4.07. Naalasite is trigonal, space group R32, with cell parameters: a = 8.494(4), c = 26.430(13) Å, V = 1651.5(4) Å3 and Z = 9. The structure, refined to R1 = 3.78% for 641 I > 2σI reflections, is based on a loose 3D framework of alternating AsO3OH tetrahedra and AlO6 octahedra. The structure is topologically equivalent to that of nafeasite and can be regarded as its Al analogue, even though nafeasite is monoclinic with space group C2.

Keywords

naalasitenew mineralarsenateframeworkcrystal structurenafeasiteRaman spectroscopyTorrecillas mineChile

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Type
Article
Information
Mineralogical Magazine , Volume 88 , Issue 2 , April 2024 , pp. 155 - 161
Copyright
Copyright © The Author(s), 2024. Published by Cambridge University Press on behalf of The Mineralogical Society of the United Kingdom and Ireland

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Footnotes

Associate Editor: Charles A Geiger

References

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