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The dense hydrous-magnesium silicate phase D, which has the ideal formula Mg[Si.sub.2][H.sub.2][O.sub.6], may be an important link in a chain of hydrous phases that carry [H.sub.2] O in the ultramafic portions of subducting lithosphere, into the Earth's lower mantle. We have synthesized a new Al-rich form of phase D, containing up to 50 wt% [Al.sub.2][O.sub.3], using a multi-anvil device at ~1300[degrees]C and 25 GPa. The phase, with the formula [Mg.sub.0.2][Fe.sub.0.15][Al.sub.1.8][H.sub.1.8]Si[O.sub.6], was initially produced in a bulk composition designed to synthesize Al- and Fe-rich magnesium silicate perovskite with a composition similar to that produced in experiments on mid-ocean ridge basalt bulk compositions at lower mantle conditions. Further experiments using a starting mixture based on the composition of this Al-rich phase resulted in the synthesis of 60-70 [micro]m long single crystals at similar conditions. The recovered crystals were slightly richer in [H.sub.2]O ([Mg.sub.0.2][Fe.sub.0.12][Al.sub.1.5][Si.sub.0.92][H.sub.3.1][O.sub.6]) and their unit-cell parameters were similar to those of Mg[Si.sub.2][H.sub.2][O.sub.6] phase D. A refinement of the crystal structure was carried out in the P[bar.3]1m space group and revealed a more disordered cation distribution than magnesium silicate phase D. All cation-oxygen distances are similar, suggesting a high degree of Si/Al disorder. Although the stability field of this new variant of phase D is yet to be determined, this phase may be an important host for [H.sub.2]O within portions of subducted oceanic crust in the lower mantle. Keywords: Lower mantle, high pressure, subduction, single crystal, DHMS, deep water cycle DOI: 10.2138/am.2010.3462

The low-temperature behavior of a natural kalsilite (ideal formula KAlSi[O.sub.4]) with P31c symmetry has been investigated by in situ single-crystal diffraction. A series of intensity data collections and structural refinements have been performed at 298, 250, 200, 150, and 100 K on decreasing temperature, and 175, 225, and 275 K on increasing T. The variations of the unit-cell parameters of kalsilite as a function of Tare continuous, and show no evidence of any phase transitions or thermo-elastic anomalies in this temperature range. An expansion is observed along [0001] with decreasing temperature. The axial and volume thermal expansion coefficients ([[alpha].sub.j] = [l.sup.-1.sub.j] x [partial derivative][l.sub.j]/[partial derivative]T, [[alpha].sub.V] = [V.sup.-1] x [partial derivative]V/[partial derivative]T) between 298 and 100 K, calculated by weighted linear regression through the data points, are [[alpha].sub.a] = [[alpha].sub.b] = 1.30(6) x [10.sup.-5], [[alpha].sub.c] = -1.5(1) x [10.sup.-5], [[alpha].sub.V] = 1.1(2) x [10.sup.-5] [K.sup.-1]. The main structural change on decreasing temperature is a cooperative anti-rotation of tetrahedra forming the six-membered rings lying parallel to (0001). This tetrahedral rotation is coupled with a change in the distances between the extra-framework cations and the framework O atoms. A small decrease in the tetrahedral tilts perpendicular to [0001] is responsible for the negative thermal expansion along [0001]; the implications of these mechanisms for thermal expansion in nephelines and kalsilites are discussed. Keywords: Kalsilite, feldspathoids, low temperature, single-crystal X-ray diffraction, thermal expansion DOI: 10.2138/am.2010.3478

Rengeite, [Sr.sub.4]Zr[Ti.sub.4][([Si.sub.2][O.sub.7]).sub.2][O.sub.8], is a Sr-analog mineral of perrierite and occurs as an accessory mineral in natrolite, pectolite, and itoigawaite veins associated with jadeitic rock from Ohmi-Itoigawa region, Japan. The symmetry of this mineral is reported to be monoclinic. Here, we found an orthorhombic polymorph of rengeite that occurs as micro domains up to 5 [micro]m in width in monoclinic rengeite crystals using electron diffraction and high-resolution TEM analyses. X-ray diffraction analysis using a Gandolfi camera also revealed the presence of the orthorhombic phase in monoclinic rengeite crystals. The unit-cell dimensions of the orthorhombic polymorph are a = 14.0, b = 5.7, c 21.9 [Angstrom], V = 1748 [[Angstrom].sup.3], and Z = 4. Although the space group of orthorhombic polymorph of rengeite has not been determined, the possible space group is Pbca or a similar one from theoretical consideration by Ito (1950). The chemical composition was determined by ATEM-EDS analysis to be Si[O.sub.2] = 22.5, Ti[O.sub.2] = 30.2, SrO = 39.4, [Nb.sub.2][O.sub.5] = 0.2, [Fe.sub.2][O.sub.3] 0.3, and Zr[O.sub.2] = 7.5, totaling 100.1 wt%, and the ideal chemical formula is [Sr.sub.4]Zr[Ti.sub.4][([Si.sub.2][O.sub.7]).sub.2][O.sub.8]. Detailed HRTEM imaging revealed that the unit cell of the orthorhombic polymorph of rengeite can be interpreted as a superstructure of monoclinic rengeite, accompanied by repeated twinning on (001) plane. The HRTEM images taken were consistent with the simulated images. Keywords: Rengeite, perrierite, polymorph, jadeite, HRTEM

This paper describes a multi-technique approach to the complete crystal-chemical characterization of a gadolinite-(Y) sample found in a volcanic holocrystalline ejectum near the Vico lake (Latium, Italy). Gadolinite-(Y) occurs as poly-twinned crystals forming rounded short-prismatic aggregates (generally 0.1-0.3 mm in size, with the largest ever found >1 mm), associated with zircon, thorite, danburite, betafite, and tourmaline. Both the chemical and the structural characterization of gadolinite-(Y from Vico required nonstandard procedures. After correction for (100) twinning, the structure of a crystal with unit-cell dimensions a = 4.7708(4) [Angstrom], b = 7.6229(7) [Angstrom], c = 9.8975(9) [Angstrom], [beta] = 90.017(7)[degrees], and V = 359.95(6) [[Angstrom].sup.3] was refined in the [P2.sub.1]/c space group down to R = 2.3%. Electron microprobe (EMP) analyses failed to give accurate quantification of major elements, due to the presence of light and volatile elements as well as of rare earth elements (REE) and actinides. Secondary ion-mass spectrometry (SIMS) analysis done with accurate calibrations on well-characterized minerals allowed quantification of light, volatile, REE, and actinide elements, and also of Ca and Si. The derived chemical composition was interpreted with reference to the site-scattering values obtained from single-crystal structure refinement. The resulting unit formula is [([Ca.sub.0.81][REE.sub.0.66][Y.sub.0.39][Th.sub.0.13] [U.sub.0.02]).sub.[SIGMA]2.01][([Fe.sup.2+.sub.029][Li.sub.0.14] [([Fe.sup.3+.sub.0.12][Mn.sub.0.02][Mg.sub.0.01]).sub.[SIGMA]0.58] [([Si.sub.1.98][Be.sub.1.09][B.sub.0.81][Li.sub.0.12]).sub.[SIGMA]4.00] [O.sub.8][([O.sub.1.20][F.sub.0.51][OH.sub.0.29]).sub.[SIGMA]2.00], which yields a calculated density of 4.267 g [cm.sup.-3]. Fourier transform infrared spectroscopy (FTIR) single-crystal spectrum of gadolinite-(Y) shows several absorptions in the OH-stretching region that can be assigned to the different local configurations involving Ca and (REE,Y) at the A site and Be, B, and Li at the Z site. Lithium incorporation in gadolinite-group minerals is proposed to occur according to the exchange vectors: (1) [sup.X][Fe.sup.2+] + [sup.A]Y [right arror] [sup.X]Li + [sup.A](Th + U) and (2) [sup.Z]Be + [sup.X][Fe.sup.2+] [right arrow] [sup.Z]Li + [sup.X][Fe.sup.3+]; the maximum amount of Li allowed in the gadolinite structure is 1.0 apfu. This work provides the first evidence that Li is a significant component in gadolinite-group minerals, particularly in geochemical environments enriched in actinides. This conclusion suggests that materials having the composition of Li-rich gadolinite may be considered as possible forms for radioactive waste disposal. Keywords: Gadolinite, lithium, single crystal XRD, EMPA, SIMS, IR spectroscopy

Dingdaohengite-(Ce), ideally [Ce.sub.4][Fe.sub.2][Ti.sub.2][Ti.sub.2][([Si.sub.2][O.sub.7].sub.2][O.sub.8], is a new member of the chevkinite group minerals from the world-famous Bayan Obo REE-Nb-Fe Mine near Baotou city, Inner Mongolian Autonomous Region, North China. It occurs in the magnesian skarn in the excontact of granite within dolomitic marble. Most individual crystals vary from 0.2 to 1.0 cm in length. Associated minerals are diopside, tremolite, richterite, allanite-(Ce), magnetite, ilmenite, spinel, titanite, pyrochlore, F-rich phlogopite, fluorapatite, quartz, and fluorite, etc. Dingdaohengite-(Ce) is probably of bimetasomatic origin among Ca-Mg-carbonate rock and/or carbonatite, and REE-, F-rich postmagmatic hydrothermal solutions. The mineral is black and becoming brown black in thin fragments. It is translucent to opaque with a submetallic-metallic luster, and a brown streak. It is brittle with conchoidal fracture. No cleavage or parting is observed. Its hardness is [VHN.sub.25g] 606.0-717.4 kg/[mm.sup.2] (Mohs hardness near 5.9). The measured density is 4.83(7) g/[cm.sup.3] and the calculated density is 4.88(0) g/[cm.sup.3]. Its reflectance vahies (for [lambda] = 589 nm) are 11.4-12.5%. It is biaxial negative. The strongest six X-ray diffraction lines in the powder pattern [d in [angstrom], (1) (hkl)] are 2.7524 (100)(121), 2.7263(98)(313), 3.1978(68)(212), 2.5460(54)(304), 2.8702(52)(020), and 3.1622(46)(312). An electron-microprobe analysis on the crystal used to collect X-ray intensity data for crystal-structure refinement gives [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], sum 99.48 wt%; the [Fe.sub.3+]/[Fe.sup.3+] ratio was converted by Mossbauer spectroscopy. The empirical formula [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] based on 22 O atoms with prevalence of Ti in the C1 site of the structure. Dingdaohengite-(Ce) is monoclinic, a = 13.4656(15) [Angstrom], b = 5.7356(6) [Angstrom], c = 11.0977(12) [Angstrom], [Beta] = 100.636(2)[degrees], V= 842.39(46) [[Angstrom].sup.3], and Z= 2. The crystal structure of dingdaohengite-(Ce) was refined with space groups [P2.sub.1]/a and C2/m. Pseudo-extinction was round, i.e., reflections with h + k = 2n are systematically strong, while those with h + k = 2n + 1 are weak, which show that the true space group of dingdaohengite-(Ce) is [P2.sub.1]/a (pseudo-C2/m). Keywords: Dingdaohengite-(Ce), [P2.sub.1]/a (pseudo-C2/m) space group, chevkinite subgroup, new mineral, Bayan Obo, China

Thermodynamic calculations of ion-exchange reactions were applied for clinoptilolite in a natural state and after irradiation with three doses of [beta]-radiation ([10.sup.12], [10.sup.15], x [10.sup.16] e/[cm.sup.2]) and [gamma]-radiation (70 Mrad). Samples were equilibrated with binary systems of [K.sup.+] [left and right arrow] [Na.sup.+] and [Cs.sup.+] [left and right arrow] [Na.sup.+] at 25[degrees] and a total normality of 0.025 N. Selectivity for K was not affected after [beta]-radiation with doses of [10.sup.12] and [10.sup.15] e/[cm.sup.2] ([DELTA]G[degrees] = -6.37 kJ/equiv, lnK[alpha] = 2.58 for the original clinoptilolite), whereas it increased considerably after 70 Mrad of [gamma]-radiation ([DELTA]G[degrees] = -7.88 kJ/equiv, lnK[alpha] = 3.18). Selectivity for [Cs.sup.+] increased for the clinoptilolite irradiated with [beta]-radiation ([10.sup.12], [10.sup.15], 3 x [10.sup.16] e/[cm.sup.2]) and [gamma]-radiation (70 Mrad). [DELTA]G[degrees] and lnK[alpha] for original sample and [Cs.sup.+] [left and right arrow] [Na.sup.+] were -7.33 kJ/equiv and 2.96, respectively. Irradiated samples with [beta]-radiation [10.sup.12], [10.sup.15], 3 x [10.sup.16] e/[cm.sup.2] and 70 Mrad [gamma]-radiation yielded [DELTA]G[degrees] and lnK[alpha]-7.41, -8.83, -8.60, -8.25 kJ/equiv and 2.99, 3.57, 3.47, 3.33 for [Cs.sup.+] [left and right arrow] [Na.sup.+], respectively. Remarkable amorphization of clinoptilolite was observed after exposure at the highest dose of [beta]-radiation (3 x [10.sup.16] e/[cm.sup.2]) with a concomitant decrease in cation-exchange capacity (CEC). Crystallographic parameters and especially exchangeable cation site coordinates were refined for all samples with the Rietveld method. Cesium-saturated samples exhibited changes in the cation sites Cs2 and Cs3, which are next to clinoptilolite channel walls with lower [Al.sup.3+] for [Si.sup.4+] substitution. The observed changes include a shift in cation sites Cs2 and Cs3 toward channel walls and occupancy decrease in site Cs2. Keywords: Clinoptilolite, ion exchange, [beta]-radiation, [gamma]-radiation, thermodynamics, Rietveld refinement

Resonant ultrasound spectra of a single crystal and a polycrystalline sample of lawsonite [Ca[Al.sub.2][Si.sub.2][O.sub.7][(OH).sub.2]* [H.sub.2]O] have been measured at room temperature and at low temperatures in the region 20-300 K. The influence of known phase transitions at 125 and 270 K is seen in the frequency variations of the resonance peaks, which are indicative of elastic stiffening, and in values for the quality factor [Q.sub.QF], which are indicative of dissipation. Two dissipation peaks, at ~250 and ~210 K, are interpreted as being due to the proton order-disorder processes associated with the two species of hydrogen atoms in the structure: one in hydroxyl OH groups and one in the [H.sub.2]O molecules. These occur below the Cmcm [left and right arrow] Pmcn transition point but coincide with changes in the shear elastic constants and in features of IR spectra reported elsewhere. A third, much smaller, dissipation peak occurs immediately below the Pmcn [left and right arrow] P[2.sub.1]cn transition point. The combination of these anomalies in acoustic dissipation and in elastic constants is consistent with the view that the Cmcm [left and right arrow] Pmcn transition is driven both by displacive and proton ordering effects. For the Pmcn [left and right arrow] P[2.sub.1]cn transition, dissipation and the transition are more closely related, consistent with the view that the transition is driven essentially by proton ordering. Keywords: Lawsonite, resonant ultrasound spectroscopy, dissipation, proton ordering

The structural behavior of thomsonite compressed in aqueous medium up to 3 GPa was studied by means of in situ synchrotron powder diffraction with a diamond anvil cell. In the range between 0.0001 and 2 GPa, the compressibility of thomsonite is markedly lower than that reported previously, where a non-penetrating medium (with only 6% [H.sub.2]O) was used. This indicates a pressure-induced hydration (PIH), which results in the transition to an over-hydrated phase observed at 2 GPa. The structure of over-hydrated thomsonite contains one additional, half-occupied [H.sub.2]O position, coordinated by the calcium at the Ca2 site, with a scolecite-like coordination [Ca[O.sub.4][([H.sub.2]O).sub.3]]. The appearance of new [H.sub.2]O position causes a 4.5% volume expansion through the cooperative rotation of [[[T.sub.2][O.sub.5]].sup.[infinity]] chains, leading to the enlargement of the cross-section of the main channels parallel to c axis. The observed deformation mechanism is similar to that found in high-hydrated and super-hydrated natrolite, although only a half of the channels are affected by PIH. The present data indicate that the over-hydration effect in fibrous zeolites strongly depends on the partial water pressure in compressing medium. Keywords: Zeolite, thomsonite, high pressure, compressibility, phase transition, crystal structure, over-hydration

Yakovenchukite-(Y), [K.sub.3]NaCa[Y.sub.2][[Si.sub.12][O.sub.30]][([H.sub.2]O).sub.4], is a new REE silicate found in a thin (3-4 cm) sodalite-aegirine-microcline veinlet cutting ijolite-urtite at Mt. Kukisvumchorr, Khibiny alkaline massif, Kola Peninsula, Russia. The mineral occurs as small prismatic crystals in intimate association with microcline, aegirine, calcite, catapleiite, donnayite-(Y), fluorapophyllite, fluorite, galena, lead, litharge, molybdenite, natrolite-gonnardite, pyrochlore, rinkite, strontianite, and vuorijarvite-K. Yakovenchukite-(Y) is creamy to colorless, with vitreous luster. The streak is white. The mineral is transparent, non-fluorescent. The Mohs hardness is about 5. The mineral is brittle. Cleavage is perfect on {100}, distinct on {010}, fracture is stepped. Densities are 2.83 g/[cm.sup.3] (measured by sink/float in heavy liquids) and 2.72 g/[cm.sup.3] (calculated). Yakovenchukite-(Y) is biaxial (+): [n.sub.[alpha]] = 1.520(5), [n.sub.[beta]] = 1.525(5), [n.sub.[gamma]] = 1.538(5) (589 nm), 2 V(meas.) = 60 [+ or -] 5[degrees], 2V(calc.) = 61.86[degrees]. The optical orientation is Y = c, X = a, Z = b, pleochroism is not observed. Chemical analysis by electron microprobe (wt%): [Na.sub.2]O 4.32, [K.sub.2]O 10.73, CaO 3.42, [Y.sub.2][O.sub.3] 15.49, [Ce.sub.2][O.sub.3] 0.10, [Dy.sub.2][O.sub.3] 0.68, [Er.sub.2][O.sub.3] 0.88, [Tm.sub.2][O.sub.3] 0.18, [Yb.sub.2][O.sub.3] 1.53, Th[O.sub.2] 0.62, Si[O.sub.2] 57.55, [H.sub.2]O (by the Penfield method) 4.70, total 100.20. The empirical formula (based on Si = 12 apfu) is [([K.sub.2.85][Na.sub.0.15]).sub.[SIGMA]3.00][Na.sub.100][([Ca.sub.0.71] [Na.sub.0.00]).sub.[SIGMA]1.31[([Y.sub.1.72] [Yb.sub.0.10][Er.sub.0.06][Dy.sub.0.05][Th.sub.0.03][Ce.sub.0.01] [Tm.sub.0.01][Ca.sub.0.05]).sub.[SIGMA]2.03 [[Si.sub.12][O.sub.30.02]] x 3.27 [H.sub.2]O. According to single-crystal X-ray study yakovenchukite-(Y) is orthorhombic, Pcca, a = 14.972(8), b = 14.137(7), c = 14.594(8) [Angstrom], V = 3089(3) [[Angstrom].sup.3], Z = 4. The strongest lines of the X-ray powder diffraction pattern ate [[d.sub.bs]([Angstrom])([I.sub.obs])(hkl)]: 7.00 (40) (020), 6.57 (60) (102), 4.20 (50) (222), 3.337 (100) (331), 3.248 (90) (024), 3.101 (40) (142), 3.014 (80) (422), 2.608 (40) (404). The crystal structure of yakovenchukite-(Y) belongs to a new structure type of minerals and inorganic compounds. It is based on microporous octahedral-tetrahedral framework of Si[O.sub.4]-tetrahedra and Y[O.sub.6]-octahedra. Silicate tetrahedra share corners to form unprecedented [[Si.sub.l2][O.sub.30]] sheets consisting of 4-, 6-, and 14-membered rings. The sheets are parallel to (001) and are linked into 3D framework through Y[O.sub.6] octahedra. [Ca.sup.2+], [K.sup.+], and [Na.sup.+] cations are located within the framework cavities. The octahedral-tetrahedral framework possess channels extended along the a axis. The channel dimensions are 4.9 x 6.2 [Angstrom], which means the free crystallographic diameter of 2.2 x 3.5 [Angstrom], that allows classifying yakovenchukite-(Y) as a microporous material. Yakovenchukite-(Y) is the latest low-temperature hydrothermal mineral, formed by alteration of earlier REE-rich minerals (pyrochlore, rinkite, etc.). The mineral is named in honor of Victor N. Yakovenchuk, a mineralogist at the Geological Institute of the Kola Science Centre of the Russian Academy of Sciences, for his outstanding contribution to the mineralogy of alkaline and alkaline-ultrabasic massifs. Keywords: Yakovenchukite-(Y), new mineral, REE-silicate, crystal structure, ultra-alkaline hydrothermal vein, Khibiny massif, Kola Peninsula

[Li.sub.0.52][Mg.sub.0.96][Sc.sub.0.52][Si.sub.2][O.sub.6] orthopyroxene was synthesized by the flux method and its structure studied with single-crystal X-ray diffraction. The crystal is orthorhombic with space group Pbca and unit-cell parameters a = 18.259(5), b = 8.883(2), c = 5.271(1) [[Angstrom].sup.3], and V= 854.9(3) [[Angstrom].sup.3]. The structure refinement shows that the M1 and M2 sites are occupied by (0.48 Mg + 0.52 Sc) and (0.48 Mg + 0.52 Li), respectively. While the 03-03-03 kinking angle (165.40[degrees]) of the silicate tetrahedral A chain appears to be normal when compared with reported data, the kinking angle (151.92[degrees]) of the B chain is the largest of all orthopyroxenes examined at ambient conditions. This is the first orthopyroxene structure that contains more than 50% trivalent and monovalent cations in the M1 and M2 sites, respectively, and displays a kinking angle of the tetrahedral B chain that is greater than 150[degrees]. Our study demonstrates the stability of the new pyroxene structure type predicted by Pannhorst (1979) at room temperature. Keywords: [Li.sub.0.52][Mg.sub.0.96][Sc.sub.0.52][Si.sub.2][O.sub.6], orthopyroxene, crystal structure, X-ray diffraction

Zincalstibite, a new mineral occurring within the cavities of marble of the Apuan Alps, Tuscany, Italy, has chemical formula [Zn.sub.2]AlSb[(OH).sub.12], space group P[bar.3], a = 5.321(1), c = 9.786(2)[Angstrom]. It is associated with sub-millimeter tufts of white crystals of minletite and sub-millimetric stalactite aggregates of opal and an amorphous copper-silicate phase (possibly crisocolla). The crystals are trigonal prismatic, with forms (110), (001),elongated [001], generally less than 10 x 10 x 40 + 50 [micro]m, with few larger crystals. They are colorless, transparent, with vitreous luster, white streak and {001} cleavage. The stronger reflections are [(hkl), d ([Angstrom]), [I.sub.rel]: (002). 4.904, 100: (100). 4.620, 35; (101), 4.179.57: (103, 110). 2.669,31;(112.11[bar.2]), 2.343,88;(114, 17[bar.4]), 1.805, 57. Zincalstibite is structurally related to cualstibite, as evidenced by the structural determinations and refinements we present ]\/r both the minerals. They are built up by layers of isolated Sb[(OH).sub.6], octahedra alternating along c with trioctahedral layers, which contain Zn and Al cations and Cu and Al cations in zincalstibite and cualstibite, respectively. In cualstibite the ordering of Al and Cu within these trioctahedral layers results in a supercell, with [a.sub.cual] = 9.150(2) [Angstrom] [approximately equal to] [square root of 3] [a.sub.zinc] The name of zincalstibite is related to its chemical composition and points to its relationships with cualstibite. Both the mineral and its name were approved by the IMA Commission for New Minerals and Mineral Names (IMA 1998-033). Keywords: Zincalstibite, cualstibite, new mineral, crystal structure, XRD data

Melanophlogite, a clathrasil, possesses a framework of corner-linked silica tetrahedra forming framework cavities that can enclose small guest molecules. Synchrotron X-ray diffraction experiments of the guest-free melanophlogite have been conducted at pressures up to 12 GPa and temperatures up to 1473 K. Upon compression at room temperature, melanophlogite gradually lost its crystallinity and became completely X-ray amorphous at ~8 GPa. The amorphization process was similar to those of denser silica polymorphs, but it reached completion at a much lower pressure (e.g., quartz becomes X-ray amorphous at ~30 GPa). The decreased amorphization pressure of melanophlogite may be attributed to its lower framework density and the ease of bending of its Si-O-Si linkages, thereby accelerating the collapse of the structure under high pressure. Determination of cell volumes of melanophlogite prior to its amorphization yielded a room-temperature bulk modulus of 26.3 [+ or -] 1.7 GPa, which is consistent with the relatively large compressibilities reported for the structurally similar zeolites. When heated at -8 GPa, the amorphous phase started to crystallize at 873 K into coesite, the stable silica phase at these pressure and temperature conditions. Thus the occurrence of pressure-induced amorphization in melanophlogite appears to result from the kinetic hindrance to its transformation to the thermodynamically stable coesite. Keywords: Melanophlogite, clathrasil, pressure-induced amorphization, compressibility, synchrotron X-ray diffraction

The single-crystal elastic properties of [Ca.sub.0.07][Mg.sub.1.93][Si.sub.2][O.sub.6] orthopyroxene (space group Pbca) have been investigated by Brillouin spectroscopy at ambient conditions. The aggregate bulk and shear moduli, ([K.sub.0,S] = 102.5 GPa (1.5) and p. = 74.2 GPa (1.1), respectively, are ~5% and ~3% lower than commonly accepted values for MgSi[O.sub.3] end-member ([K.sub.0,S] = 107.6, [mu] = 76.8 GPa). These results indicate that the incorporation of small amount of Ca in the orthoenstatite structure does not greatly affect its elastic properties. As a consequence, the increase in bulk modulus reported in natural orthopyroxenes relative to the Mg-end-member is not related to the substitution of Ca in the M2 octahedral sites, but more probably to the substitution of A1 in tetrahedral sites. Keywords: Brillouin spectroscopy, elastic properties, enstatite, orthopyroxene

Various silica-based microreactors have been designed that use enzyme immobilization to address technical concerns in proteolysis including inefficient and incomplete protein digestion. Most of current designs for proteolytic reactors can improve either protease stability or proteolysis efficiency of individual protein(s). However, the desired features such as rapid digestion, larger sequence coverage, and high sensitivity have not been achieved by a single microreactor design for broad range proteins with diverse physical properties. Here, unlike conventional enzyme immobilization strategies, we describe a novel proteolytic nanoreactor based on the unique three-dimensional nanopore structure of our newly synthesized mesoporous silica (MPS), FDU-12, which integrates substrate enrichment, 'reagent-free' protein denaturation, and efficient proteolytic digestion. In our design, protein substrates were first captured by MPS nanopore structure and were concentrated from the solution. Following the pH change and applying trypsin, the denaturation and concurrent proteolysis of broadrange proteins were efficiently achieved. In minutes, many more sample peptides from the in-nanopore digestion of protein mixtures were detected by mass spectrometry, resulting in the identifications of a broad range of diverse proteins with high sequence coverage. The unique features of FDU- 12 nanostructure that allow rapid, complete proteolysis and resulting enhanced sequence coverage of individual proteins were investigated by using Raman spectroscopy and comparative studies with respect to other MPSs.

We have undertaken a detailed analysis of the X-ray photoelectron spectra obtained from the three polymorphs of [Al.sub.2]Si[O.sub.5]; andalusite, sillimanite, and kyanite. Comparison of the spectra was made based on the chemical bonding and structural differences in the Al- and Si-coordination within each polymorph. The spectra for Si(2p) for all three polymorphs are nearly identical, consistent with the fact that all the Si atoms are in 4-fold (tetrahedral) coordination, whereas the binding energies, peak shapes, and peak widths for Al(2p) vary depending on the type of polymorph. The upper-valence band for all three polymorphs is characterized by four main features derived from O(2p), Al(3s), Al(2p), Si(3s), and Si(3p), and the differences in their contributions are observed. The density of state of the [Al.sub.2]Si[O.sub.5] polymorphs is relatively featureless compared to those observed from [alpha]-Si[O.sub.2] and [alpha]-[Al.sub.2][O.sub.3], suggesting that the orbital overlaps span a greater range in energy. The observed band gap energy for [Al.sub.2]Si[O.sub.5] (sillimanite) was ~9.1 eV, a value in between those for [alpha]-Si[O.sub.2] (~8.6eV) and [alpha] - [Al.sub.2][O.sub.3] (-9.6eV). The conduction band feature of [Al.sub.2]Si[O.sub.5] was experimentally compared to those of [alpha]-Si[O.sub.2] and [alpha]-[Al.sub.2][O.sub.3], and shown that it is indeed intermediate between the [alpha]-Si[O.sub.2] and [alpha]-[Al.sub.2][O.sub.3] phases. Keywords: [Al.sub.2]Si[O.sub.5] polymorphs, X-ray photoelectron spectroscopy, low electron energy loss spectroscopy, valence- and conduction band structures, andalusite, sillimanite, kyanite

Mullite (Mul) formation after high-T muscovite (Ms) breakdown has been studied in phyllosilicate-rich bricks. At T [greater than or equal to] 900[degrees]C Ms dehydroxylation is followed by partial melting that triggers the nucleation and growth of Mul acicular crystals. An analytical electron microscopy study reveals that the Mul is a 3:2-type with a [sup.[6]][([Al.sub.1.686][Ti.sub.0.031][Fe.sub.0.159] [Mg.sub.0.134)].sup.[4]]([Al.sub.2.360][Si.sub.1.649])[O.sub.9.82] formula and an O atom vacancy of x = 0.18. This is consistent with X-ray diffraction results [i.e., unit-cell parameters: a = 7.553(7), b = 7.694(7), and c = 2.881 (1) [Angstrom], V = 167.45 [[Angstrom].sup.3]]. The initial stage of the process resulting in Mul growth followed the balanced reaction Ms [right arrow] 0.275Mul + 0.667Melt + 0.244[K.sub.2]O + 0.01[Na.sub.2]O + 0.125[H2.sub.2]O, yielding an alkali-poor peraluminous melt. [H.sub.2]O with K (and Na), which are lost along the (001) planes of dehydroxylated Ms, playa significant role as melting agents. The c-axes of the Mul crystals are oriented parallel to [[010].sub.ms] or to the symmetrically equivalent [.sub.ms] zone axis, while the [(120).sub.mul] or [(210).sub.mul] planes are subparallel to [(001).sub.ms] (TEM results). These systematic orientations point to epitaxial Mul nucleation and growth on the remaining Ms substrate, which acts as a template for Mul heterogeneous nucleation. Randomly oriented Mul growth is also observed during the late stages of the process (i.e., melt cooling). The epitaxial nature of Mul growth after dehydroxylated Ms melting minimizes the energy requirement for nucleation. In addition, the water released after Ms breakdown and the multicomponent nature of the melt enable this high-T aluminum silicate to grow at T ~ 900[degrees]C, almost 100[degrees]C below the Si[O.sub.2]-[Al.sub.2][O.sub.3]-[K.sub.2]O ternary system eutectic (after a melt with an end-member Ms composition).

A density-functional theory was used to compute all the independent elastic constants of coesite, a high-pressure polymorph of silica, as functions of pressure up to 15 GPa. Coesite were found to be similar to quartz and exhibited a gradual softening of a shear modulus [B.sub.44] with increasing pressure, in contrast to the rising bulk modulus.

Mesoporous SBA-16 and SBA-15 are studied to control their possible morphologies and SBA-16 is synthesized using a silicon source (tetraethoxysilane, TEOS) and a ternary system consisting of surfactant F127 (EO106PO70EO106), water and butanol. The formation and size of these macrospheres are controlled by variations in the silica concentration.