Volume 84, Issue 7-8

Medical questions surrounding the toxicity of “silica” and other silicon-containing materials introduced into the body can be answered only through use of microanalytical techniques that provide chemical and structural analyses of microscopic and submicroscopic particles. A useful approach to the study of minerals and other foreign substances associated with silicone breast implants is to use polarized-light optical microscopy to pinpoint the materials of interest in the tissue and to follow that observation with analysis by Raman spectroscopy. Silicone breast implants contain both the organic polymer silicone and particles of amorphous silica. We studied the breast tissue from six women who had silicone breast implants and from three controls who never had implants to address questions about post-implant alteration, such as to “crystalline SiO 2 .” Optical analysis of the mammary tissue sections revealed a variety of birefringent and non-birefringent, non-cellular materials. Raman spectroscopic analyses of those substances identified many similar materials in tissue from women with and without silicone implants: calcite, apatite, starch, lipid, and β-carotene. We also spectroscopically identified silicone (only in breast tissue from patients recognized to have had ruptured implants) and paraffin (only in one sample that had been embedded in paraffin and subsequently “deparaffinized”). In tissue sections of 5 μm thickness (standard thickness of pathology sections), it is impossible to detect optically the birefringence of quartz (or any other form of crystalline SiO 2 ), even though it may be possible to image such thin crystalline SiO 2 grains in polarized light due to light-scattering phenomena. Moreover, neither crystalline nor amorphous silica was identified by Raman spectroscopy in the tissue sections. Review of the pathology literature on such materialsbased issues as silicosis and calcification revealed some misapplication of the optical microscopy term “birefringence” and misleading identifications of minerals in tissue sections. Our conclusion is that useful collaborations can be developed between (1) pathologists who observe foreign materials in tissue sections and understand the medical context of their findings and (2) mineralogists who routinely use optical, chemical, and structural analyses to characterize micrometer-sized crystalline materials and who understand materials properties.

Quartz-one of the most abundant minerals in the Earth’s crust-has been deemed a human carcinogen by the International Agency for Research on Cancer (IARC), with the main threat to humans being lung cancer through inhalation of dust particles. Currently, the United States Environmental Protection Agency (EPA) has required communities to monitor PM10 (particulate matter less than 10 micrometers in diameter) levels, with the concern that higher levels of PM10 have been linked to increased respiratory disease rates. This hypothesis can be tested by an analysis of mortality data for groups that have received high lifelong exposures to quartz-rich PM10 (e.g., farmers). Idaho is a very dusty state with a large agricultural community and can serve as a model to test this hypothesis. A database was constructed of PM10 levels statewide and of all the deaths attributed to respiratory diseases in Idaho from 1969 to 1994. For the Moscow, Idaho, PM samples, quartz composed approximately 10% of the PM10, with the remainder being 30% feldspar and 60% Mount St. Helens volcanic ash. The PM2.5 samples contained no detectable mineral matter. Statewide, the quartz component for the PM10 samples ranged from 7 to 16%. Analysis of the database indicates that Idaho residents, in general, have below-average lung cancer rates when compared to the U.S. population and that Idaho farmers are at no greater risk of dying from lung cancer than non-farmers. These conclusions are based upon age- and smoking-adjusted standard mortality ratios (SMRs). No correlations or trends between PM10 levels and respiratory diseases could be found in the general population. Data for chronic obstructive pulmonary diseases (COPDs) are more difficult to interpret because of fewer deaths and the inability to compensate for the effect of smoking in the induction of these diseases; however, it appears that Idaho has a higher rate of COPDs when compared to the U.S. populations and that farmers have a higher rate of COPDs than non-farmers.

The chemical composition of spinel was determined for a suite of 19 diogenites (orthopyroxenites) thought to be from asteroid 4 Vesta. Previous studies (Fowler et al. 1994, 1995) of orthopyroxene demonstrated that these diogenites are linked genetically, perhaps through fractional crystallization, in one or more crustal intrusions. The present study focuses on spinel to see if it also retains some chemical signatures of an igneous history. The chemical compositions across spinel grains reveal flat concentration profiles, indicating major subsolidus exchange with orthopyroxene. Nevertheless, significant chemical differences exist among the average spinel compositions from individual diogenites in the suite. A chemical continuum exists from high-Cr, low-Al spinel in diogenite LAP 91900 (Cr 2 O 3 60.7 wt%; Al 2 O 3 6.1 wt%) to low-Cr, high-Al spinel in diogenite ALHA 77256 (Cr 2 O 3 44.7 wt%; Al 2 O 3 21.8 wt%), which may represent one or more fractionation series. In these trends, Al and Ti behave as incompatible elements whose abundances increase with crystallization. These systematics differ from those in spinel in terrestrial or lunar basaltic systems because of the extremely Al-depleted nature of the diogenite parental melts. In terrestrial and lunar basalts, the increase in Al concentration in spinel is interrupted when plagioclase crystallizes. In diogenite parental melts, plagioclase does not come onto the liquidus until the very end of spinel crystallization.

Cathodoluminescence (CL) microscopy and spectroscopy of single plagioclase grains from lunar soil show that plagioclases from Luna 20 (highland) have more or less homogeneous CL with both blue or green colors, whereas plagioclase grains sampled by Luna 24 (mare) luminesce dominantly green with partially distinct oscillatory zoning. The three main emission bands in the blue (~450 nm), green (~560 nm), and red-IR (~690 nm), mimic the most common emission bands in terrestrial feldspars. Mn 2+ is the most important activator element in lunar plagioclases. Variations in the amount of structurally incorporated Mn 2+ cause variations in the intensity of the green emission band at 560 nm, in some cases resulting in zoning of the CL intensity within single crystals. Calculations by a combination of quantitative spectral analysis of CL emission and PIXE measurements yield Mn concentrations of 7-47 ppm. The intense intrinsic emission band at 450 nm (probably an Al-O - -Al center), which was especially prominent in Luna 20 plagioclases, causes their blue CL color. The occurrence of a CL emission band at ~690 nm in plagioclases from Luna 24 samples confirms that Fe 3+ -activated CL is common in these grains. The results indicate that at least some of the Fe in Luna 24 plagioclases is Fe 3+ , whereas all Luna 20 plagioclases have Fe 3+ -near the CL detection limit of about 0.1 ppm.

A magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopic study was done on the series of synthetic gallian-fluor amphiboles to identify the extent of Ga and Si ordering in the tetrahedral sites. Assignment of the peaks in the complex 29 Si MAS NMR spectra of pargasitic amphiboles is based on observations of the gradual change in peak intensity and position as well as by comparison with computer simulations of the relative intensities of the 29 Si MAS NMR spectra for the amphiboles along the compositional join. The 29 Si spectra agree best with models that allow Ga on both the T1 and T2 sites, which supports the previous cation distribution results obtained by Rietveld refinement of powder X-ray diffraction data. It was not possible, however, to discriminate between cation distribution models that allowed completely random mixing of Ga and Si vs. the presence of Ga-O-Ga avoidance on the tetrahedral sites. Comparison of the very high speed 71 Ga MAS NMR spectra (35 kHz) with the distribution of Ga in octahedral and tetrahedral sites shows that the ratio of tetrahedral to octahedral site occupancy is vastly overestimated from the NMR spectra due to the large quadrupolar effects of the asymmetrical octahedral site. The 23 Na MAS NMR spectra of tremolite and Ga-substituted pargasites show a shift to higher frequency and increasing peak width with Ga content that can be related to the reduction in magnetic shielding produced by the substitution of Ga for Si and Mg.

Raman spectra and lattice dynamics calculations are presented for the dioctahedral mica, muscovite. Calculated fundamental mode frequencies for the Raman-active and A g and B g species were fit to observed fundamentals assigned to features in the two polarized Raman spectra collected, so that unambiguous vibrational assignments could be made to most peaks in the Raman data. Calculated frequencies for the IR-active A u and B u modes generally fall within the frequency ranges of bands in the IR spectra for muscovite presented earlier. Factor group analysis indicates that motion from all atom types in the muscovite structure can be found in modes for all four vibrational species. Force constant values determined for muscovite are similar to equivalent values calculated for the trioctahedral mica, phlogopite. Raman and IR-active modes calculated at frequencies greater than 800 cm -1 are dominated by internal sheet T-O stretch and T-O-T bend motions, where T is a tetrahedral site. Modes between 800 and 360 cm -1 have internal tetrahedral sheet motions mixed with K and octahedral Al displacements. Modes at frequencies less than 360 cm -1 have lattice and OH motions. Inter-sheet bonding in the muscovite structure is strong enough to affect modes at frequencies as high as 824 cm -1 .

Analysis of divalent Co, Zn, Pb, and Ba XAFS spectra of synthetic and natural calcite samples containing trace concentrations of these heavy metals confirms their substitution in the unique Ca site in octahedral coordination with varying degrees of local distortion. The existence of each trace metal at the single site in the bulk crystal is significant in view of previous studies showing that these trace elements are incorporated differentially at multiple, structurally distinct surface sites occurring in nonequivalent growth steps on calcite surfaces. The octahedral coordination for Ba is particularly noteworthy because of its large size (35% larger than host Ca) and the fact that it rarely exists as a major constituent with such a low coordination number. Analysis of the local distortion and relaxation around the impurities shows a nearly complete contraction of the structure around Co 2+ and Zn 2+ . The Co-O and Zn-O first-shell distances are only slightly longer than in CoCO 3 and ZnCO 3 , with a site compliance of ~80-90%. Displacements of higher shells relative to those in calcite decrease rapidly, but irregularly, over a short distance, and the relaxation may be largely confined within 6-7 Å of the impurity. The dilation around the large Pb 2+ and Ba 2+ ions in calcite also shows a high degree of site compliance (85-90%). Relaxation around Pb and Ba also appears to be restricted, but extending further for Ba than for Pb. The limited observations suggest that compliance of the octahedral site in calcite is larger than for the cation site in the rocksalt structure. The high compliance for the metal site in calcite may reflect the corner-sharing topology of the structure and is also probably the reason that calcite shows such a wide range of isovalent substitutions in nature. The findings also provide a direct indication of the local strain associated with a dilute substitutional solid solution.

STM images of hematite (α-Fe 2 O 3 ) (001) surfaces taken under a wider variety of conditions than in previous studies are presented. The results strongly suggest that only Fe sites contribute to the tunneling current. Specifically, corrugated unit-cell structures expected of the Fe sublattice are observed under both occupied- and unoccupied-states imaging conditions. A pattern of apparent vacancies was observed under conditions previously attributed to oxygen states; this is most simply interpreted either as Fe vacancies, or Fe sites whose electronic structure has been altered by a (unknown) coordinating anion, but difficult to explain as the oxygen sublattice. For unoccupied states imaging, decreasing the tip-sample distance (increasing the tunneling current) results in an image change from only one site per unit cell to three sites per unit cell. This is also relatively easy to explain using the Fe sublattice, but difficult to explain using the oxygen sublattice. These results are modeled using resonant tunneling theory, which shows that changes in bias voltage, tunneling medium, and tip-sample distance can have the observed effects only if Fe atoms are being imaged. The results have implications for modeling electron transfer across mineral-water interfaces more generally because they provide a framework for understanding site-specific electron transfer kinetic parameters.

XANES measurements on gold-bearing arsenian pyrite from the Twin Creeks Carlin-type gold deposits show that gold is present as both Au 0 and Au I+ and arsenic is present at As I- . Au 0 is attributed to sub-micrometer size inclusions of free gold, whereas Au I+ is attributed to gold in the lattice of the arsenian pyrite. STEM observations suggest that As I- is probably concentrated in angstrom-scale, randomly distributed layers with a marcasite or arsenopyrite structure. Ionic gold (Au I+ ) could be concentrated in these layers as well, and is present in both twofold- and fourfold-coordinated forms, with fourfold-coordinated Au I+ more abundant. Twofold-coordinated Au I+ is similar to gold in Au 2 S in which it is linearly coordinated to two sulfur atoms. The nature of fourfold-coordinated Au I+ is not well understood, although it might be present as an Au-As-S compound where gold is bonded in fourfold coordination to sulfur and arsenic atoms, or in vacancy positions on a cation site in the arsenian pyrite. Au I+ was probably incorporated into arsenian pyrite by adsorption onto pyrite surfaces during crystal growth. The most likely compound in the case of twofold-coordinated Au I+ was probably a tri-atomic surface complex such as S pyrite -Au I+ -S bi-sulfide H or Au I+ -S-Au I+ . The correlation between gold and arsenic might be related to the role of arsenic in enhancing the adsorption of gold complexes of this type on pyrite surfaces, possibly through semiconductor effects.

To elucidate the process and mechanism of the prograde conversion of saponite to chlorite through corrensite, the microstructures of a series of chlorite-smectite (C-S) mixed-layer samples from Kamikita, northern Japan were examined by high-resolution transmission electron microscopy using both lattice and structure imaging. Corrensite grows epitaxially as domains of 5-20 nm thick mainly within homogeneous saponite domains, without forming randomly interstratified C-S. Then, chlorite domains grow outside homogeneous corrensite domains without forming randomly interstratified C-S or chloritecorrensite (C-Co), and finally are predominant. An atomic resolution image suggests that corrensite essentially consists of the 1 M stacking of alternating chloritic and smectitic layers. The structure and occurrence suggest corrensite is mineralogically a unique species. Comparison of the stacking vectors of corrensite along [001] to those of chlorite reveals that the stacking sequence is not inherited during the process from corrensite to chlorite. We rarely observed layer terminations of the hydroxide sheets both in corrensite and chlorite domains, and the layer terminations that do exist can be explained as defects rather than the formation of corrensite or chlorite. Our data strongly suggest that the saponitetochlorite conversion series progresses stepwise from saponite to corrensite and from corrensite to chlorite, and that the dominant reaction mechanisms are dissolution and precipitation.

Incommensurate modulation in ganophyllite crystals was investigated with selected-area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), analytical electron microscopy (AEM), and single-crystal X-ray diffraction (XRD) techniques. The XRD data were used to perform a new subcell (a = 5.550 Å, b = 13.539 Å, c = 25.134 Å, β = 93.928°) refinement of the structure with a higher precision than previous refinements (R = 0.041). Although supercell reflections were too weak for collection with the diffractometer, the supercell was modeled by comparing experimental SAED patterns and HRTEM images to their simulated counterparts. These simulations indicate that incommensurate modulation arises from offsets in the location of inverted tetrahedra between adjacent [100] strips. The true supercell of incommensurate crystals involves a tripling of the subcell a axis and at least a twelvefold increase in the b axis; previously identified supercell reflections are actually aggregates of extremely closely spaced reflections in incommensurate crystals. Unlike commensurate crystals, the subcell c axis of incommensurate ganophyllite is not doubled. AEM data suggest that the occurrence of commensurate or incommensurate forms is not compositionally dependent.

Several minerals and inorganic compounds contain (XA 4 ) tetrahedra, with anions, X (O 2- , N 3- , and F - ), as central atoms and cations, A (Cu 2+ , Zn 2+ , Pb 2+ , Bi 3+ , REE 3+ , etc.), as ligands. These tetrahedra are well defined in these crystal structures because the bond valences between A and X are essentially higher than the bond valences between A and atoms from other structural units. According to their size, anion-centered tetrahedra may be subdivided into large and small tetrahedra, formed from cations with ionic radii near to 1.0 Å (e.g., Pb 2+ , Bi 3+ , and REE 3+ ) and 0.5-0.7 Å (e.g., Cu 2+ and Zn 2+ ), respectively. The small anion-centered tetrahedra prefer to link through corners, whereas the large tetrahedra prefer to link through edges. When the tetrahedra are built from both “small” and “large” cations, “small” cations prefer to be corners shared between lesser numbers of tetrahedra and not involved in linking tetrahedra via edges. The general crystal-chemical formula of minerals and compounds containing anion-centered tetrahedra may be written as A' k [X n A m ][A p X q ]X' l , where [X n A m ] (usually n ≤ m) is a structural unit based on anion-centered tetrahedra (ACT) and [A p X q ] (p < q) is a structural unit based on cation-centered polyhedra (CCP). A' is a cation that does not belong to anion- or cation-centered polyhedra; it is usually an interstitial cation such as an alkali metal; X' is an interstitial anion such as halide or S 2- . Structures containing both ACT and CCP units may be ordered according to the values of their dimensionality. In structures without CCP units, an important role is played by large interstitial anions that link finite ACT units, chains, or layers into threedimensional structures or fill cavities in ACT frameworks.

Diffuse X-ray scattering from single crystals of metamict zircon reveals residual crystallinity even at high fluences (up to 7.2 × 10 18 α-decay events/g). The experimental evidence does not suggest that radiation-induced amorphization is a “phase transition.” The observations are in good agreement with a nonconvergent, heterogeneous model of amorphization in which damage production is a random process of cascade formation and overlap at increasing fluence. Instead of an amorphization transition, the existence of a percolation transition is postulated. At the level of radiation damage near the percolation point, the heterogeneous strain broadening of Xray diffraction profiles is reduced whereas the particle-size broadening increases. Simultaneously, the macroscopic swelling of the zircon becomes larger than the maximum expansion of the unit-cell parameters. A suitable empirical parameter that characterizes this transition is the flux, D s , at which the macroscopic expansion is identical to the maximum expansion of the crystallographic unit cell. In zircon, D s = 3.5·10 18 α-decay events/g.

Burbankite, ideally (Na,Ca) 3 (Sr,REE,Ba) 3 (CO 3 ) 5 , is a rare REE carbonate mineral that until now had been encountered only at a few localities including highly alkaline silicate rocks, carbonatites, and lacustrine sediments. It was identified as an abundant solid phase in fluid inclusions that represent fluids derived from the Kalkfeld carbonatite complex (Namibia). Burbankite occurs in association with other solids including nahcolite, halite, sylvite, rouvilleite (?), fluorite, calcite, cryolite, base metal sulfides, and phosphates. The carbonatite-derived fluids were trapped in quartzite country rocks close to the carbonatite contact. The optical and geochemical identification of burbankite has been confirmed by confocal Laser Raman spectrometry. The burbankite crystals show a Raman shift at 1078 cm -1 , which is significantly displaced relative to peaks for other common carbonates and is much broader. The elemental composition of burbankite was determined by a combination of SEMEDX on opened inclusions and synchrotron-XRF analysis on unopened wafers. The SEM-EDX analyses of the burbankite crystals yielded a compositional range (in wt%) of Na 2 O 10.6-17.5, CaO 3.6-17.4, SrO 12.0-26.7, BaO 2.5-5.5, La 2 O 3 3.5-7.0, Ce 2 O 3 4.7-9.0, Nd 2 O 3 0.9-2.1, and CO 2 (calc.) 29.8-35.2. The Na/Ca ratios are between 1.0 and 4.3, which is high in comparison with rock-forming burbankite occurrences, and clearly distinguishes the burbankite crystals from carbocernaite. Synchrotron micro-XRF spectra yielded REE patterns decreasing from La to Yb over 2.5 orders of magnitude with small negative Eu anomaly [(Eu/Eu*) cn = 0.5-1.0] in some cases. The Y/Ho ratios range from 1 to 5, and Th/U ratios are between 1 and 10. The fluids trapped are interpreted to represent a highly evolved but pristine, alkali-rich, hydrous, carbonate melt, which had not lost alkalis to the country rocks by fenitization processes. The common occurrence of burbankite crystals in the fluid inclusions shows the high capability of carbonate melts and fluids to transport high-field-strength and large-ion-lithophile elements.

Single crystals (0.1-0.5 mm) of natural heulandite from Nasik (India) were treated in 4 M NaCl solution at 423 K for 12 weeks, yielding almost fully Na-exchanged heulandite (composition: Na 8.44 Ca 0.09 K 0.01 [Al 8.63 Si 27.37 O 72 ]·nH 2 O). This precursor phase was subsequently treated in a Teflon autoclave with 0.5 M rare-earth element (REE) solution (0.25 M ErCl 3 ·6H 2 O and 0.25 M LaCl 3 ·7H 2 O; pH of 2.8) for 15 weeks also at 423 K. Er and La in the zeolite were subsequently measured by inductively coupled plasma (ICP) mass spectrometry yielding only 656 ppm Er and 195 ppm La, whereas electron-microprobe (EMP) analyses indicated that the Na concentration decreased from originally 8.44 Na pfu to 0.25 Na pfu. The low REE content may be explained by the relatively small free diameter of the channel windows and the large size of hydrated REE ions. The low Na concentration is caused by partial dealumination of the tetrahedral framework where Si replaced some Al of the framework and Al migrated into the structural channel. Dealumination or more generally dissolution phenomena on the crystal surface occurring due to the acidic milieu in the exchange solution were observed as etch pits on scanning-electron microscope (SEM) images. X-ray single-crystal data of REECl 3 -treated heulandite were collected at 100 and 293 K and at 100 K after partial dehydration at 323 and 378 K. Structure refinement using all data sets suggested the presence of low concentrations of octahedrally coordinated Al 3+ that was dissolved from the framework and incorporated into the channels. T-O distances in the framework, corrected for rotational disorder, are significantly shortened compared with the Na-exchanged precursor heulandite. This indicates that REECl 3 -treated heulandite has a significantly lower Al concentration in the framework than the Na-exchanged precursor phase.

Six single crystals of Mg 3 (Mg x Si x Al 2-2x )Si 3 O 12 with x = 0.05, 0.13, 0.24, 0.38, 0.52, and 0.64 (the majorite solid-solution) were synthesized at 20 GPa and 2000 °C with a “6-8” type uniaxial splitsphere apparatus. Single-crystal X-ray diffraction studies revealed discontinuities in compositional dependence of the molar volume, equivalent isotropic temperature factors (B eq ), and mean bond lengths between x = 0.24 and 0.38. Single crystals in the compositional range 0 ≤ x ≤ 0.24 show no birefringence, whereas those of x = 0.64 have a slight optical anisotropy. Moreover, the cell symmetry for x = 0.64 obtained using synchrotron X-ray radiation is tetragonal with a slight deviation from cubic. On the basis of site splitting expected from compositional dependence of B eq obtained by cubic refinement, the most probable space group in the range 0.38 ≤ x ≤ 0.64 is I4 1 /acd (tetragonal), which is the maximal subgroup of the space group Ia3̅d (cubic). Given that the previous reports that crystals with 0.8 ≤ x ≤ 1.0 have the tetragonal space group I4 1 /a, the majorite solid-solution in this system undergoes the series of symmetry changes, Ia3̅d →I4 1 /acd→I4 1 /a, with increasing MgSiO 3 component. The symmetry changes from Ia3̅d to I4 1 /acd cannot be explained by the cation ordering on the octahedral site. Strong electrostatic interaction between the dodecahedral (Mg 2+ ) and tetrahedral (Si 4+ ) cations was observed from atomic thermal motion and electron density distribution. Because one of the site symmetries of the two nonequivalent tetrahedral sites in I4 1 /acd structure loses the center of symmetry with the symmetry reduction from Ia3̅d to I4 1 /acd, the symmetry reduction may be caused by the electronic polarization of the cations due to the neighboring cation-cation interaction.

The crystal structure of albite from Stintino, Sardinia, Italy, was refined at different degrees of disorder to determine the (Si-Al) order-disorder process. Eight X-ray structure refinements were performed on single-crystal data collected at room temperature, after heating at 1050-1090 °C for 3 to 12 days. Average long-range order coefficients S between 0.93 and 0.24 were obtained for different samples. The results indicate that in the (Si-Al) disordering process Al enriches the T1m site more than T2o and T2m sites. This trend continues until both T1o and T1m are occupied by 30% of Al, and T2o and T2m by 20% of Al. No evidence of complete disorder in T1 and T2 sites has been experimentally found to date. The (Si-Al) disordering process induces a clockwise rotation of the four-membered rings of tetrahedra parallel to the (100) plane. An inverse linear relationship between the isotropic equivalent displacement parameter of the Na atom, B eq (Na), and S is interpreted as positional disorder of Na. The variations in the Na-O bond lengths with increasing disorder are explained by the related variations in the bond strengths of tetrahedral cations.

Boralsilite, Al 16 B 6 Si 2 O 37 , is monoclinic, space group C2/m, with a = 14.767(1), b = 5.574(1), c = 15.079(1) Å, β = 91.96(1)°, and Z = 2. The structure was solved with direct methods and refined to an unweighted residual of 0.026 using 1193 observed reflections. The structure is closely related to those of sillimanite, andalusite, grandidierite, synthetic aluminum borate (Al 18 B 4 O 33 ), and werdingite. These structures are all based on a backbone of chains of edge-sharing AlO 6 octahedra arranged parallel to c (≅ 5.6 Å) and at the vertices and center of a pseudo-tetragonal subcell having a ≅ b ≅ 7.5 Å. In the boralsilite structure, AlO 6 octahedral chains are cross-linked by Si 2 O 7 disilicate groups, BO 4 tetrahedra, BO 3 triangles, and AlO 5 trigonal bipyramids. A given BO 4 or SiO 4 tetrahedron or BO 3 triangle shares two vertices with two adjacent AlO 6 octahedra of one chain and a third vertex with an octahedron vertex of an adjacent chain, thus cross-linking the AlO 6 octahedral chains. Further linkage is provided through vertex-sharing of AlO 5 trigonal bipyramids. These bipyramids alternate with B or Si polyhedra parallel to AlO 6 octahedral chains to form four kinds of cross-linking chains of polyhedra, with alternate atom pairs [5] Al1-Si, [5] Al2- [4] B2, [5] Al3- [3] B1, and [5] Al4- [3] B3. The units which cross-link between chains of AlO 6 octahedra can alternatively be viewed as consisting of Si 2 O 7 dimers, trimers of edge-sharing AlO 5 trigonal bipyramids (plus a B triangle and B tetrahedron), and dimers of edge-sharing AlO 5 trigonal bipyramids (plus B triangles and tetrahedra), Variations on these themes are found in the structures of sillimanite, andalusite, grandidierite, werdingite, mullite, and synthetic Al 18 B 4 O 33 . The interchangeability and variety of the various interchain units appears to result in part from the flexibility produced by the ability of Al and B to assume a variety of coordinations by oxygen and from the potential for partial vacancy of some anion and cation sites.

Aluminum-rich titanites [Ca(Ti,Al)(O,F)SiO 4 ] with X Al > 0.53 [X Al = Al/(Al+Ti)], including the pure end-member CaAlFSiO 4 , were synthesized for the first time in a high-pressure experimental study. The crystal structure of CaAlFSiO 4 was determined by Rietveld analysis of an X-ray powder diffraction pattern. CaAlFSiO 4 is monoclinic, belongs to the space group A2/a, and has the unit-cell dimensions a = 6.9149(2) Å, β = 8.5064(1) Å, c = 6.4384(2) Å, and b = 114.684(2)°. The unit-cell volume is less than 93% of CaTiOSiO 4 , which is consistent with the natural occurrence of Al-rich titanite in high-P rocks. Although previous studies suggested that titanite with X Al > 0.5 is possibly not stable, this study demonstrates that complete solid solution occurs between CaTiOSiO 4 and CaAlFSiO 4 . The similarity of the crystal structures of titanite and CaAlFSiO 4 explains why in natural Al-rich titanite the end-member CaAlFSiO 4 generally dominates over the hypothetical end-member CaAlOHSiO 4 , which under geological conditions is stable in a different crystal structure.

Kanemite was studied by single-crystal X-ray diffraction. The mineral, ideally NaHSi 2 O 5 ·3H 2 O, is orthorhombic (space group Pbcn); unit-cell parameters are a = 4.946(3), b = 20.502(15), c = 7.275(3) Å, with Z = 4. The structure is solved and refined to an R value of 0.058 for 825 independent reflections. The arrangement of atoms consists of alternating (010) sheets of corrugated [Si 2 O 4 OH] n n- and hydrated Na. The silicate sheets contain six-membered rings of HOSiO 3 -SiO 4 units. Sodium atoms coordinate to six water molecules, forming layers of distorted octahedra. Residual electron densities were located that give reasonable positions for four H atoms. One H is part of a silanol group, and the other three H atoms are associated with water bonded to Na. Bonding between the silicate and Na sheets is through hydrogen bonding from H of the Na layer to O of the silicate sheet.

Polarized IR-absorption spectra were measured on inclusion-free spots, 50 μm in diameter of (100)-, (010)-, and (001)-oriented single-crystal plates of orthorhombic cordierites extracted from anatectic granitoids and their pegmatite from the western part of the Ukrainian shield. In the range 3100-2700 cm -1 , the spectra display four weak (α lin ≤ ca. 7 cm -1 ) and sharp (∆ν 1/2 ≅ 20 cm -1 ) bands typical of the antisymmetric and symmetric stretching modes of CH 3 - and -CHH 2 - groups of aliphatic hydrocarbons, C n H 2n+2 (ν as,CH₃ at 2951-2959 cm -1 , ν as,CH₂ at 2920-2923 cm -1 , ν sym,CH₃ at 2871-2874 cm -1 , ν sym,CH₂ at 2850-2851). All bands are polarized in the ac-plane of orthorhombic cordierite. In the temperature range 123 ≤T (K) ≤573, the degree of polarization decreases as temperature increases. The band polarizations and their temperature dependence ensure that the hydrocarbons are incorporated in the cordierite matrix, i.e., in the ca. 5.8 Å wide cavities of the c-parallel channels of the crystal structure. The concentrations of alkanes, C n H 2n+2 from band intensities, are between about 20 and about 100 ppm, corresponding to about 0.7·10 -3 and about 2.3·10 -3 molecules per formula unit cordieriite. Evaluation of the averaged intensities of the antisymmetric as well as symmetric C-H stretching vibrations of either species, CH 3 - and -CH 2 - , yields a ratio of 1:1 between them consistent with n = 4 only, realized in butane C 4 H 10 or in a butane-rich mixture with n = 4 on average and concentrations between 0.7 × 10 -3 to 2.3 × 10 -3 molecule pfu. Polarizations as well as molecular and cordierite-cavity sizes are consistent with an allocation of butane molecules in the channel cavities of the cordierite structure, with the molecular axes of butane predominantly parallel to b.

The 35 Cl NMR spectroscopy of Cl - -intercalated hydrotalcite and the Ca-aluminate hydrate hydrocalumite (Friedel’s salt) demonstrates dynamical behavior of interlayer Cl - , the presence of dynamical order-disorder phase transitions in these phases, and significant differences in the transition temperatures and temperature interval over which the transitions occur. In hydrocalumite, the Ca,Al distribution is ordered, the interlayer water is directly coordinated to Ca in the hydroxide layer (creating sevenfold-coordinated Ca), and the interlayer Cl - and water sites are well ordered. The 35 Cl NMR data show that the interlayer Cl - site has uniaxial or nearly uniaxial symmetry above about 0 °C and reduced (triaxial) symmetry at lower temperatures. Differential scanning calorimetry (DSC) data show this change to be due to a structural phase transition at about 6 °C. The NMR and XRD data suggest that this phase transition is due to dynamical order-disorder involving a rigid interlayer atomic arrangement at low temperatures and dynamically averaged interlayer species at high temperatures. In contrast, in hydrotalcite Mg and Al are disordered over the octahedral sites, and the interlayer is disordered. The 35 Cl NMR data for it show poorly resolved signal indicating a range of Cl⁻ environments and a change from triaxial to uniaxial or nearly uniaxial symmetry at Cl⁻ occurring over a broad temperature interval below -40 °C. DSC data for our sample shows a broad and poorly defined endothermic anomaly in the -100 to -75 °C range. These data suggest the presence of a phase transition that occurs over a larger temperature range due to its disordered interlayer structure. The results suggest that similar variable temperature NMR behavior previously observed for interlayer cations in smectites can be thought of as due to comparable phase transitions that lack well-defined critical temperatures due to the disordered interlayer structures.

Three- and five-quantum 17 O MAS NMR experiments are used to resolve fully the three crystallographically distinct oxygen species in forsterite (Mg 2 SiO 4 ). The chemical shift and quadrupolar parameters extracted from these spectra are compared with the literature values obtained using conventional 17 O MAS and dynamic-angle-spinning (DAS) NMR.