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

Marsaalamite-(Y), ideally Y(MoO4)OH, is a new molybdate mineral discovered in<br>the greisenized Um Safi F-rich granite located in the Marsa Alam District, Central<br>Eastern Desert of Egypt. It typically occurs as inclusions in or intergrowths with F-rich<br>zinnwaldite. It forms micaceous aggregates, with sizes varying from 0.1 to 1 mm.<br>Marsaalamite-(Y) is non-magnetic, white in color, and has an earthy lustre and white<br>streak. It is brittle (34 Mohs) and has basal cleavages {001}. The calculated density is<br>4.90 g.cm–3 based on the empirical formula and unit-cell parameters refined from X-ray<br>powder diffraction data. Marsaalamite-(Y) is associated with arsenopyrite, baryte,<br>bastnäsite-(Ce), cassiterite, chernovite-(Y), columbite-(Fe), fluocerite-(Ce), fluorite, iron<br>oxy-hydroxides, löllingite, molybdenite, monazite-(Ce), pyrite, quartz, rutile, thorite,<br>wolframite, wulfenite, xenotime-(Y), and several unidentified phases. The empirical<br>2<br>formula is (Y0.67Er0.10Dy0.08Yb0.08Ho0.02Lu0.02Tm0.02Ca0.01)Σ1.00 (Mo0.95S0.03As0.01P0.01)Σ1.00<br>O4.00[(OH)0.88F0.11Cl0.01]Σ1.00; the ideal end member formula is Y(MoO4)(OH). The<br>presence of a hydroxyl group has been confirmed by Raman and infrared spectroscopy,<br>and its concentration has been calculated from the stoichiometry. Marsaalamite-(Y) is the<br>natural (OH)-dominant analogue of synthetic Y(MoO4)F. It is monoclinic, space group<br>P21/c, with unit-cell parameters a = 5.1863(7) Å, b = 12.3203(11) Å, c = 6.6953(7) Å, β<br>= 114.173(8)°, V = 390.30(8) Å3, and Z = 4. Extreme fractionation of the parental<br>halogen-rich, A-type granitic magma triggered the greisenization of the granite. The<br>marsaalamite-(Y) occurred simultaneously with or immediately after the crystallization<br>of F-rich zinnwaldite based on the textural relationship. Therefore, the crystallization of<br>marsaalamite-(Y) was most likely controlled by fluid-induced processes rather than<br>magmatic conditions. The new mineral was approved by the Commission on New<br>Minerals, Nomenclature and Classification of the International Mineralogical Association<br>(CNMNC-IMA) (IMA 2024-050) and named after the Marsa Alam District, Al-Bahr Al- Ahmer Governorate, Egypt