Chukhrovite-(Ce), (Ca ₃ Ce)[AlF ₆ ] ₂ (SO ₄ )F·12H ₂ O, from the Tripi mine, Alì, Messina Province, Sicily, Italy: definition of neotype material

ABSTRACT Neotype material of chukhrovite-(Ce), ideally (Ca 3 Ce)[AlF 6 ] 2 (SO 4 )F·12H 2 O, was established on the basis of a new occurrence from the Tripi mine, Alì, Peloritani Mountains, Sicily, Italy. In fact the Russian specimens originally considered as type material of this species were later found to correspond to Ce-rich chukhrovite-(Y). At the Tripi mine, chukhrovite-(Ce) occurs as white cube-octahedral crystals, up to 0.05 mm in size, associated with creedite, quartz and fluorite. Electron microprobe analysis gave (in wt.%, normalised to sum = 100.00): SO 3 8.40, P 2 O 5 0.16, ZrO 2 0.12, Al 2 O 3 11.95, Y 2 O 3 0.48, La 2 O 3 3.64, Ce 2 O 3 7.63, Pr 2 O 3 1.00, Nd 2 O 3 3.23, Sm 2 O 3 0.97, Eu 2 O 3 0.13, Gd 2 O 3 0.97, Dy 2 O 3 0.21, CaO 20.47, F 22.09, Cl 0.07, O = (F, Cl) –9.31, H 2 O calc 27.80. On the basis of 29 anions per formula unit, assuming the presence of 13 (F+Cl+OH) atoms and 12 H 2 O groups, the empirical formula of chukhrovite-(Ce) from the Tripi mine is Ca 3.17 (Ce 0.40 La 0.19 Nd 0.17 Pr 0.05 Sm 0.05 Gd 0.05 Y 0.04 Eu 0.01 Dy 0.01 ) Σ0.97 Zr 0.01 Al 2.04 (S 0.91 P 0.02 ) Σ0.93 O 4 [F 10.10 Cl 0.02 (OH) 2.88 ] Σ13.00 ·12H 2 O. The occurrence of H 2 O groups was supported by micro-Raman spectroscopy. Chukhrovite-(Ce) is cubic, Fd $\bar 3$ , with a = 16.7608(5) Å, V = 4708.5(4) Å 3 and Z = 8. Its crystal structure was refined to R 1 = 0.0378 for 604 unique reflections with F o > 4σ( F o ) and 36 least-square parameters. Chukhrovite-(Ce) belongs to the chukhrovite group and it is isotypic with chukhrovite-(Y), whereas it is homeotypic with chukhrovite-(Ca).