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A synthetic pyroxene with composition LiFe[Ge.sub.2][O.sub.6] and space group P[2.sub.1]/c at ambient conditions was investigated by single-crystal X-ray diffraction using a diamond anvil cell. The unit-cell parameters and crystal structure were determined at eight different pressures up to 8.7 GPa. Between 4.16 and 4.83 GPa, the sample shows a strongly first-order phase transition as indicated by a drastic drop in a, c, [beta], and unit-cell volume. The transition is marked by the disappearance of b-type reflections (h + k = odd) forbidden in a C-centered lattice. The volume bulk modulus of the P[2.sub.1]/c phase is estimated to be 110 GPa as compared to 147 GPa of the C2/c one. The crystal structure evolution as a function of pressure is mainly influenced by the kinking of tetrahedral chains; the A and B non-symmetry equivalent chains of the P[2.sub.1]/c phase undergo strong deformations up to 4.16 GPa (A chain ~2%, B chain ~5.3%). At the transition, the two chains become symmetry equivalent and the single tetrahedral chain of the C2/c phase shows only minor deformations with pressure (~1.9%) due to its already strong kinking (~130 [degrees]). Such behavior is the main reason for the strong difference in compressibility between the low- and high-symmetry forms. Keywords: Single-crystal structure analysis, germanates, high-pressure phase transformations, X-ray diffraction

Aluminocerite-(Ce), ideally [(Ce,Ca).sub.9]Al[(Si[O.sub.4]).sub.3] [[Si[O.sub.3](OH)].sub.4][(OH).sub.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 rhombohedral 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.sup.3]. It is uniaxial, optically positive, with [n.sub.o] = 1.810-1.816 and [n.sub.e] = 1.812-1.822 ([lambda], = 589 nm) and non-pleochroic. The average of 15 electron microprobe analyses for the holotype gave (wt%): [Ce.sub.2][O.sub.3] 23.37; [Nd.sub.2][O.sub.3] 15.59; [La.sub.2][O.sub.3] 7.43; [Sm.sub.2][O.sub.3] 4.38; [Pr.sub.2][O.sub.3] 3.54; [Gd.sub.2][O.sub.3] 3.12; [Y.sub.2][O.sub.3] 1.68; [Dy.sub.2][O.sub.3] 0.46; [Yb.sub.2][O.sub.3] 0.07; CaO 8.31; [Fe.sub.2][O.sub.3] 0.47; [Al.sub.2][O.sub.3] 2.47; Si[O.sub.2] 24.01; and [H.sub.2]O 3.63 (calculated from crystal-chemical constraints), total 98.53 wt%, corresponding to the empirical formula [([Ca.sub.2.60][Ce.sub.2.49][Nd.sub.1.62][La.sub.0.80][Sm.sub.0.44] [Pr.sub.0.38][Gd.sub.0.30][Y.sub.0.26][Dy.sub.0.04][Yb.sub.0.01]).sub.[SIGMA] 8.94][([Al.sup.3+.sub.0.85][Fe.sup.3+.sub.0.10]).sub.[SIGMA]0.95] [(Si[O.sub.4]).sub.3][[Si[O.sub.3](OH)].sub.4] [(OH).sub.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].sup.3]. The strongest eight lines in the X-ray powder diffraction pattern are [d in [Angstrom] (I)(hkl)]: 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). Keywords: Aluminocerite-(Ce), single-crystal XRD, EMP analyses, new mineral, Raman spectroscopy

Abstract: The equation of state for γ-Fe2SiO4 was determined by single-crystal X-ray diffraction up to 10.2GPa at room temperature. The pressure–volume data, measured at 10 different pressures, do not show any evidence of a phase transformation and were fit by a third-order Birch–Murnaghan equation of state. The following coefficients were refined simultaneously: V 0 =559.44(6)Å3, K T0 =187.3(1.7)GPa, and K′=5.5(4). This result implies that the Mg/Fe substitution along the γ-Fo–Fa join does not significantly affect the bulk modulus. The sample shows higher K′ than other compositions along the Fo–Fa join, which generally have K′∼4. Based on our results we can calculate the sound bulk velocity of γ-Fe2SiO4 up to the pressures of the Transition Zone. Due to the larger K′ of γ-Fe2SiO4, the difference in bulk sound velocity between the two end-members decreases with increasing pressure. [ABSTRACT FROM AUTHOR]