Aluminocerite-(Ce), ideally (Ce,Ca)(9)Al(SiO4)(3)[SiO3(OH)](4)(OH)(3), is isostructural with cerite-(Ce) and cerite-(La). The holotype was found at the Ratti quarry, near Baveno, Italy, in millimeter-sized secondary cavities hosted in aplite-pegmatite veins and pods within pink granite. Aluminocerite-(Ce) forms aggregates of pseudo-octahedral to rhornbohedral crystals flattened on the c axis. The cotype of aluminocerite-(Ce) was discovered at the Locatelly quarry, also near Baveno, where it Occurs in centimeter-sized miarolitic cavities in pink granite. The mineral is pale pink to pink-reddish, with a white streak, and is translucent with a vitreous luster. Aluminocerite-(Ce) is non-fluorescent. The hardness based on the Mohs scale is 5, and the tenacity is brittle. Neither cleavage, fracture, or twinning were observed. Calculated density is 4.675 g/cm(3). It is uniaxial, optically positive, with n(o) = 1.810-1.816 and n(e) = 1.812-1.822 (lambda = 589 nm) and non-pleochroic. The average of 15 electron microprobe analyses for the holotype gave (wt%): Ce2O3 23.37; Nd2O3 15.59; La2O3 7.43; Sm2O3 4.38; Pr2O3 3.54; Gd2O3 3.12; Y2O3 1.68; DY2O3 0.46; Yb2O3 0.07; CaO 8.31; Fe2O3 0.47; Al2O3 2.47; SiO2 24.01; and H2O 3.63 (calculated from crystal-chemical constraints), total 98.53 wt%, corresponding to the empirical formula (Ca2.60Ce2.49Nd1.62La0.80Sm0.44Pr0.38Gd0.30Y0.16DY0.04Yb0.01)(Sigma 8.94)(Al0.853+Fe0.103+)(Sigma 0.95)(SiO4)(3)[SiO3(OH)](4) (OH)(3.06), calculated on the basis of Si = 7. Aluminocerite-(Ce) is trigonal, space group R3c, with a =10.645(1), c = 38.019(5) angstrom, V = 3731 angstrom(3). The strongest eight lines in the X-ray powder diffraction pattern are [d in angstrom (I)(hkol)}: 3.405(27)(122), 3.250(26)(124), 2.914(100)(02,10), 2.647(58)(220), 2.198(40)(03,12), 1.923(34) (238), 1.826(24)(051), and 1.732(46)(03, 18). The crystal structure has been refined to R1 = 0.056 for 745 observed reflections. The name is an allusion to the fact that it is the Al-dominant analog of cerite-(Ce).
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