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Elramlyite-(Ce), (□ 0.67 Ce 0.33 )Th 2 (PO 4 ) 2 F 3 , a new thorium phosphate fluoride from the Um Safi area, Central Eastern Desert, Egypt

Year: 2026

Type: article

Abstract: Elramlyite-(Ce), ideally (□ 0.67 Ce 0.33 )Th 2 (PO 4 ) 2 F 3 , is a new thorium phosphate fluoride from the greisenised F-rich granite in the Um Safi area, Central Eastern Desert, Egypt.It typically occurs as cryptocrystalline, porous aggregates (0.5-2 mm) mainly containing inclusions of monazite-(Ce) and opal-CT.Elramlyite-(Ce) is white, non-magnetic, with an earthy lustre and white streak, and its aggregate is highly brittle with a Mohs hardness of 2-3.The calculated density is 5.96 g•cm -3 , based on the empirical formula and unit-cell parameters refined from powder X-ray diffraction data.The empirical formula is (□ 0.50 REE 0.26 Ca 0.15 Na 0.09 ) Σ1.00 (Th 1.50 REE 0.46 Fe 3+ 0.04 ) Σ2.00 (P 1.69 S 0.29 Si 0.02 ) Σ2.00 O 8 [F 1.87 (OH) 1.13 ] Σ3.00 ; the ideal formula is (□ 0.67 Ce 0.33 )Th 2 (PO 4 ) 2 F 3 .Elramlyite-(Ce) is associated with "zinnwaldite", monazite-(Ce), fluocerite-(Ce), bastnäsite-(Ce), marsaalamite-(Y), Yb-rich xenotime-(Y), chernovite-(Y), zircon, thorite, fluorapatite, columbite-(Fe), rutile, cassiterite, hübnerite-ferberite series, opal-CT, fluorite, baryte, arsenopyrite, pyrite, löllingite, molybdenite, some unidentified arsenates and other As-bearing minerals, iron oxyhydroxides, and wulfenite.Elramlyite-(Ce) is monoclinic, space group I2/a, with unit-cell parameters a = 8.2197(5) Å, b = 6.8479(3)Å, c = 14.0806(8)Å, β = 96.304(5)°,V = 787.780(3)Å³, and Z = 4. Structurally, it is related to synthetic NaPr 2 (SO 4 ) 2 F 3 ˗, LiLa 2 (SO 4 ) 2 F 3 ˗, and LiEr 2 (SO 4 ) 2 F 3 ˗type compounds via the coupled substitutions REE 3+ + S 6+ = Th 4+ + P 5+ and (Na,Li)⁺ = 2/3□ + 1/3REE 3+ .Elramlyite-(Ce) was formed as a post-magmatic, hydrothermal phase through fluid-mediated alteration of pre-existing Th-REE-F-bearing mineral assemblages.It was approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 2025-057) and is named in honour of Mahmoud Fawzy El Ramly (1923-2016), an Egyptian mineralogist and petrologist.

Source: Mineralogical Magazine

DOI: 10.1180/mgm.2026.10242