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Marsaalamite-(Y), Y(MoO4)OH, a new molybdate mineral from the Um Safi area, Marsa Alam District, Central Eastern Desert, Egypt

Published online by Cambridge University Press:  27 December 2024

Nasser Mourad Mahdy Open the ORCID record for Nasser Mourad Mahdy [Opens in a new window] ,
Martin Ondrejka Open the ORCID record for Martin Ondrejka [Opens in a new window] ,
Peter Bačík Open the ORCID record for Peter Bačík [Opens in a new window] ,
Cristian Biagioni Open the ORCID record for Cristian Biagioni [Opens in a new window] ,
Jiří Sejkora Open the ORCID record for Jiří Sejkora [Opens in a new window] ,
Pavel Uher ,
Martin Števko Open the ORCID record for Martin Števko [Opens in a new window] ,
Hans-Jürgen Förster Open the ORCID record for Hans-Jürgen Förster [Opens in a new window]  and
Tomáš Mikuš Open the ORCID record for Tomáš Mikuš [Opens in a new window]
Nasser Mourad Mahdy*
Affiliation:
Nuclear Materials Authority, Cairo, Egypt Department of Mineralogy, Petrology and Economic Geology, Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia
Martin Ondrejka
Affiliation:
Department of Mineralogy, Petrology and Economic Geology, Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia
Peter Bačík
Affiliation:
Department of Mineralogy, Petrology and Economic Geology, Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia Earth Science Institute, Slovak Academy of Sciences, Bratislava, Slovakia
Cristian Biagioni
Affiliation:
Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy
Jiří Sejkora
Affiliation:
Department of Mineralogy and Petrology, National Museum, Prague 9, Czech Republic
Pavel Uher
Affiliation:
Department of Mineralogy, Petrology and Economic Geology, Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia
Martin Števko
Affiliation:
Earth Science Institute, Slovak Academy of Sciences, Bratislava, Slovakia Department of Mineralogy and Petrology, National Museum, Prague 9, Czech Republic
Hans-Jürgen Förster
Affiliation:
GFZ Helmholtz Centre for Geosciences, Potsdam, Germany;
Tomáš Mikuš
Affiliation:
Earth Science Institute, Slovak Academy of Sciences, Banská Bystrica, Slovakia
*
Corresponding author: Nasser Mourad Mahdy; Email: nassermahdy91@yahoo.com
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Abstract

Marsaalamite-(Y), ideally Y(MoO4)OH, is a new molybdate mineral discovered in the greisenised Um Safi F-rich granite located in the Marsa Alam District, Central Eastern Desert, Egypt. It typically occurs as inclusions in or intergrowths with F-rich zinnwaldite. It forms micaceous aggregates, with sizes varying from 0.1 to 1 mm. Marsaalamite-(Y) is non-magnetic, white in colour, and has an earthy lustre and white streak. It is brittle (3–4 Mohs) and has basal cleavages {010}. The calculated density is 4.90 g.cm–3 based on the empirical formula and unit-cell parameters refined from powder X-ray diffraction data. Marsaalamite-(Y) is associated with arsenopyrite, baryte, bastnäsite-(Ce), cassiterite, chernovite-(Y), columbite-(Fe), fluocerite-(Ce), fluorite, iron oxy-hydroxides, löllingite, molybdenite, monazite-(Ce), pyrite, quartz, rutile, thorite, wolframite, wulfenite, xenotime-(Y) and several unidentified phases. The empirical formula is (Y0.67Er0.10Dy0.08Yb0.08Ho0.02Lu0.02Tm0.02Ca0.01)Σ1.00(Mo0.95S0.03As0.01P0.01)Σ1.00O4.00[(OH)0.88F0.11Cl0.01]Σ1.00; the ideal end-member formula is Y(MoO4)(OH). The presence of a hydroxyl group has been confirmed by Raman and infrared spectroscopy, and its concentration has been calculated from the stoichiometry. Marsaalamite-(Y) is the natural (OH)-dominant analogue of synthetic Y(MoO4)F. It is monoclinic, space group P21/c, with unit-cell parameters a = 5.1863(7) Å, b = 12.3203(11) Å, c = 6.6953(7) Å, β = 114.173(8)°, V = 390.30(8) Å3, and Z = 4. Extreme fractionation of the parental halogen-rich, A-type granitic magma triggered the greisenisation of the granite. Marsaalamite-(Y) occurred simultaneously with or immediately after the crystallisation of F-rich zinnwaldite based on the textural relationship. Therefore, the crystallisation of marsaalamite-(Y) was most likely to have been controlled by fluid-induced processes rather than magmatic conditions. The new mineral has been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 2024-050) and named after the Marsa Alam District, Al-Bahr Al-Ahmer Governorate, Egypt.

Keywords

new mineralmarsaalamite-(Y)molybdatezinnwalditegreisenised graniteCentral Eastern DesertEgypt

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Article
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Mineralogical Magazine , First View , pp. 1 - 11
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: Daniel Atencio

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