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We report a FTIR (Fourier transform infrared) study of a set of cordierite samples from different occurrence and with different H2O/CO2 content. The specimens were fully characterized by a combination of techniques including optical microscopy, single-crystal X-ray diffraction, EMPA (electron microprobe analysis), SIMS (secondary ion mass spectrometry), and FTIR spectroscopy. All cordierites are orthorhombic Ccmm. According to the EMPA data, the Si/Al ratio is always close to 5:4; XMg ranges from 76.31 to 96.63, and additional octahedral constituents occur in very small amounts. Extraframework K and Ca are negligible, while Na reaches the values up to 0.84 apfu. SIMS shows H2O up to 1.52 and CO2 up to 1.11 wt%. Optically transparent single crystals were oriented using the spindle stage and examined by FTIR microspectroscopy under polarized light. On the basis of the polarizing behaviour, the observed bands were assigned to water molecules in two different orientations and to CO2 molecules in the structural channels. The IR spectra also show the presence of small amounts of CO in the samples. Refined integrated molar absorption coefficients were calibrated for the quantitative microanalysis of both H2O and CO2 in cordierite based on single-crystal polarized-light FTIR spectroscopy. For H2O the integrated molar coefficients for type I and type II water molecules (m3 modes) were calculated separately and are [I]e = 5,200 ± 700 l mol-1 cm-2 and [II]e = 13,000 ± 3,000 l mol-1 cm-2, respectively. For CO2 the integrated coefficient is eCO2 = 19,000 ± 2,000 l mol-1 cm-2.

The symmetry and crystal chemistry of a (OH,F)-rich spessartine from Junzico Xijang, Wushan Spessartine Mine, Yunxiao Co., Fujian Province, P.R. China, with composition X(Mn2þ2.87Fe2þ 0.09Ca0.04) Y(Al1.94Fe3þ0.06)Z[(SiO4)2.52 (OH1.11F0.81)] have been studied by single-crystal X-ray structure refinement and FTIR spectroscopy. This sample is tetragonal, space group I41/acd, with a ¼ b ¼ 11.6347(3) A? , c ¼ 11.6449(3) A? , c/a ¼ 1.006, Rall 3.1% (qmax ¼ 55). The two independent tetrahedra differ significantly both in terms of refined bond-lengths and site-scattering values, the latter allowing to confirm the extent of the (OH,F) substitution and to its preferential ordering at O3, the site occupied by the anions coordinated to Z2. FTIR spectra consist of a prominent peak at 3580 cm1 and a doublet at 3622-3632 cm1. Pleochroic curves suggest assignment to a unique O--H dipole, involved in two different hydrogen bonds (O3--H O2 and O3--H O3, the latter showing two different, O--H H and O--H F, configurations). The observed space group and composition imply: (a) that lowering in symmetry is related to the presence of (OH,F)4 groups; (b) the existence of a new hydrogarnet end-member with ideal composition XMn3 YAl2 Z[(SiO4)2(OH)4] and significant F content, the first related to the pyralspite series; the sample of this work is close to its 50 : 50 solid solution with spessartine. Geometric considerations and the very limited increase in volume with respect to spessartine suggest that the presence of F is a requisite for the incorporation of significant amount of monovalent anions in pyralspites.

The P21/m ¡ê C2/m phase-transition has been studied by high-T FTIR analysis on a series of synthetic amphiboles in the Li2O.Na2O.MgO.SiO2.H2O (LNMSH) system. Spectra were collected in the T range 25.450 .C on KBr disks. All examined amphiboles have P21/m symmetry at room T. Their OH-stretching FTIR spectrum consists of two main bands at ¡­ 3740 and 3715 cm.1. At the transition temperature (Tc), these bands merge into one single absorption centred at ¡­ 3720 cm.1, and no further change is observed beyond this T. Significant modifications consisting in peak shifting and band broadening are also observed in the MIR (medium infrared) 1300.640 cm.1 region. Tc values for the different compositions were estimated based on various methods; the most reliable procedure is considered to be the fit of Landau 2-4-6 potentials using band shifts observed in the MIR region. The Tc values obtained for all samples are consistent with previous results obtained on two members of the series examined here by single-crystal or synchrotron powder HT-XRD (high-T X-ray diffraction). They correlate linearly with the aggregate cation radius at M(4) [Tc (.C) = 803.533 rM(4); R2 = 0.97]. This work thus provides a measure of the role played by the size of the M(4) polyhedron in determining the Tc in simple chemical systems where the B-site occupancy (and geometry) is the only variable. The slope of the equation is far less steep in the LNMSH system than in cummingtonite; crystal-chemical reasons for this behaviour are discussed, and the local order between A and monovalent B cations is suggested to be the major constraint. In more complex systems, inspection of the available data shows that other factors such as the aggregate size of the strip of octahedra must be taken into account.

suite of well-characterized Ti-rich pargasites from Lherz (French Pyrenees). All amphiboles studied have fairly constant M-site composition, with [6]Altot ~0.55 atoms per formula unit (apfu), [6]Ti ~0.45 apfu, and [6]Fe3+ ~0.40 apfu. SIMS and SREF data show all samples to have an O3 anion composition of OH ? O2- ? 1.0 apfu, with negligible F. The FTIR spectra show for all samples a broad absorption consisting of several overlapping bands; three main components can be recognized: ~3710, 3686, and 3660 cm-1, respectively, with an asymmetric tail extending to lower frequency. Six Gaussian components can be fi tted to the spectra; comparison with spectra of both synthetic and natural pargasites allows fi ve of these components to be assigned to local confi gurations involving OH-O2- at the O3 site, thus showing that coupling with an O2- anion through an A-cation signifi cantly affects band position. Infrared spectroscopy can detect the presence of O2- in amphiboles in chemically favorable cases, i.e., in the absence of F. Moreover, the FTIR spectra show that all octahedral confi gurations involving M1Ti4+ or M1Fe3+ M3Fe3+ are associated with O2- at both adjacent O3 sites, and that M3Al is locally associated with OH, confi rming SRO models based on structure refi nement results.

This work reports the crystal-chemical characterization of Mn-rich amphiboles from the Grenville Marble of the Arnold mine, Fowler, St. Lawrence Co., New York (U.S.A.), which were previously described by Benimoff et al. (1991) as "manganoan silicic edenite." According to the new nomenclature scheme for monoclinic amphiboles (Leake et al. 2004) the ideal composition of reference, Na-A (B)(CaMn)Mg-C(5)T(Si7Al)O-22(OH)(2) with Ca > 1 apfu, is an end-member of the newly defined Group 5, and is named parvo-mangano-edenite. Re-examination of the original rock specimen showed significant inter- and intra-crystalline compositional variations, which can be expressed by the (Na-1Al-1A)-Na-A-Al-T square S-T(1)1, and (Mn2Ca-2)-Mn-B-Ca-B exchange vectors. The first vector leads to parvo-manganotremolite, ideally(A)square(B)(CaMn)(Mg5Si8O22)-Mg-C-Si-T(OH)(2) with Ca > 1. The second mechanism was never found to reach Mn dominance; however, crystal-chemical analysis does not provide any evidence of structural limits, and thus the magno-calcic counterparts of the Group 5 amphiboles of this work may occur in similar but Mn-richer genetic environments. The presence of Mn at the B site helps to stabilize the charge arrangement of edenite. The parvo-mangano-edenite crystal with composition closest to the end-member, i.e., (A)(Na0.74K0.02)(B)(Ca1.27Mn0.73)(C)(Mg4.51Mn0.282+Fe0.052+Fe0.033+Al0.12Ti0.01)(T)(Si7.07Al0.93)O-22(OH)(2), has a = 9.8260(5), b = 18.0487(9), c = 5.2840(4) angstrom, beta = 104.55(1)degrees, V = 907.1 angstrom(3) (Z = 2); the calculated density is 3.11 g/cm(3). The parvo-mangano tremolite crystal, with composition (A)(Na0.44K0.01)(B)(Ca1.13Mn0.83Na0.04)(C)(Mg Mn-4.69(0.21)2+,Fe0.032+Fe0.013+Al0.06)(T)(Si7.52Al0.48)O-22 (OH)(2), has a = 9.7807(5), b = 18.0548(9), c = 5.2928(4) angstrom beta = 104.19(1)degrees, V = 906.1 angstrom(3) (Z = 2); the calculated density is 3.08 g/cm(3). The different compositions are virtually indistinguishable under the optical microscope, but can be identified by a measure of their unit-cell parameters. The single-crystal FUR spectrum of parvo-mangano-edenite in the OH-stretching region shows two main absorptions at 3711 and 3671 cm(-1), plus shoulders at 3695, 3660, and 3641 cm(-1), respectively. FTIR spectroscopy indicates extensive short-range-order of cations in these amphiboles.

Vesuvianite is a hydrous sorosilicate with a complex composition which includes both light (H, B, F) and heavy elements, such as Rare Earth Elements (REE), Th and U. In the last few years there has been much work devoted to this mineral (e.g. Groat et al. 1992, 1994, 1996). Several aspects of its crystal chemistry, however, are not yet completely defined. For instance, the boron incorporation in the structure is known to be related to coupled substitutions involving H (Groat et al., 1994), but the possible hydrogarnet mechanism - whereby (H4O4)4- environments are created in Si-deficient samples (Galuskin et al., 2003) - is still not verified. In addition, the H-B distribution among the available sites, possibly affecting the physical (optical) properties of the mineral (Groat et al., 1994) is also not well constrained. These challenging crystal-chemical problems promoted the present work aimed at characterising a large suite of B-rich vesuvianites from Latium (Italy) by a combination of micro-beam techniques such as EMPA and SIMS, single-crystal X-ray diffraction and single-crystal, polarized radiation, Fourier-transform infrared (FTIR) spectroscopy. In this study, light and volatile elements (H, Li, Be, B, F), Y, Sr, REE and actinides (U, Th) were analysed with a Cameca IMS 4f ion microprobe (CNR-IGG, Pavia) using a 16O- primary beam of few ?m ?, at a current intensity of few nA. 1H+, 7Li+, 9Be+, 11B+ and 19F+ were investigated after degassing the crystal mount at the vacuum of ? 10-7 Pa in the ion microprobe sample chamber (together with the H standards) close to the spots previously selected for trace elements. Snarum and Durango apatite were used as standards for REE, Y, Sr; BB and LL stdB glasses for U and Th (Ottolini & Oberti, 2000). The elbaite no. 19 from Ottolini et al. (2002) was used to calibrate the ion signals for H, Li, B and F, while danalite was employed for Be. The crystal-chemical formulae were based on 18 Si atoms. As a result, the vesuvianite suite shows rather variable Mg + Fe, very low MnO contents, and TiO2 up to 1.94 wt%. Most samples are B- (up to 3.67 wt% B2O3) and F-rich (up to 2.38 wt%). The REE content is also significant with ?(REE,Y)ox. up to 4.63 wt%. Minor constituents are represented by the actinides [?(Th,U)ox up to 0.271 wt%] and BeO (up to 0.255 wt%). H2O ranges from 0.243 to 0.665 wt%. Li is present at a few hundred ppm. A calibration curve at ? 10% rel. accuracy (corresponding to 2?% error) based on SIMS data for H was used as reference for the quantitative analysis of H2O in the vesuvianite suite by polarized-radiation FTIR spectra. The resulting integrated molar absorption coefficient turned out to be ?i = 100.000? 2.000 l mol-1 cm-2, in excellent agreement with previous studies on similar matrixes (e.g. Bellatreccia et al., 2004). The data obtained by combining microchemistry with spectroscopy are also in good accord with single-crystal X-diffraction data.

Short-range order involves local clusters of atoms that occur either more or less frequently than predicted by a random distribution. Infrared spectroscopy in the principal (OH)-stretching region is sensitive to such local arrangements, and hence the (OH) group can be used as a local probe of short-range arrangements of atoms. Examination of natural amphiboles of fairly simple composition indicates that the principal (OH)-stretching frequency is sensitive to such local arrangements, generating fine structure that gives information on short-range arrangements. Moreover, the fine structure is sensitive to both nearest-neighbor and next-nearest-neighbor arrangements. The short-range arrangements that can occur are constrained by the local version of the valence-matching principle, and this helps in assignment of the bands in the fine structure of the corresponding infrared spectra. Recent results on synthetic amphiboles illustrate these issues. Monoclinic amphiboles in the systems richterite-pargasite, tremolite- pargasite and tremolite-hornblende show strong SRO involving T-, C- and A-group cations. Amphiboles involving (OH)-F solid-solution with M (vacancy) at the A site (e.g., tremolite-fluorotremolite) show one-mode behavior, whereas amphiboles with Na or K at the A site (e.g., richterite-fluororichterite) show two-mode behavior, indicating that nearest-neighbor arrangements of atoms couple through an occupied A site, but do not couple through a vacant A site. Furthermore, the relative band intensities in (OH)-F amphibole solid-solutions showing two-mode behavior indicate that (OH) and F are completely short-range disordered with respect to each other in the amphibole series examined thus far. Amphiboles in the system pargasite-fluoropargasite show strong SRO of (OH) and F with regard to the cations occupying the associated nearest-neighbor M(1)M(1)M(3) sites: arrangements involving MgMgAl-(OH) are far more common than arrangements involving MgMgAl-F. Examination of Ti-bearing richteritic amphiboles show that [4]Ti4+ and Si are short-range disordered with regard to each other. Crystal-structure refinement, SIMS analysis and local bond-valence requirements suggest that [6]Ti4+ and O(3)O2- are locally associated at adjacent M(1) and O(3) sites in (at least some) amphiboles. It is apparent that SRO is very common in monoclinic amphiboles. Although much work remains to be done to fully characterize SRO in amphiboles, the general features are already emerging, and local bond-valence requirements seem to be the (principal) factor controlling this type of order. SRO is of significance in that it will affect the stability of amphiboles (and other minerals in which it occurs) through its entropy (and enthalpy) effects; the way in which these effects can be formulated for such a complicated case is not yet clear, but what is clear is that future thermodynamic models need to consider SRO in amphiboles and probably in other minerals in which heterovalent substitutions are common.

In the present work, we characterize the amphibole Na(NaMg)Mg5Si8O22(OH)2 synthesized at 0.4 GPa and 750, 800, and 850 °C, and 0.5 GPa, 900 °C. Experiments at 800 and 900 °C yielded crystals suitable for single-crystal data collection. Structure refinement shows that synthetic Na(NaMg)Mg5Si8O22(OH)2 has P21/m symmetry at room T. The two non-equivalent tetrahedral double-chains differ in their degree of stretching and kinking. The infrared spectrum of synthetic Na(NaMg)Mg5Si8O22(OH)2 has two well-defined absorption bands at 3742 and 3715 cm-1 which can be assigned to O-H bands associated with the two independent anion sites (O3A and O3B) in the structure. The higher frequency band is assigned to the shorter O3B-H2 bond, and the lower frequency band is assigned to the longer O3A-H1 bond. The broader shape of the 3743 cm-1 band is consistent with a stronger interaction of the H2 atom with ANa, which is confirmed by structure refinement. Increasing T of synthesis causes a progressive departure from the ideal stoichiometry via the A1BMg1ANa-1BNa-1 substitution, as confirmed by EMPA, structure refinement, and FTIR spectroscopy.

This work reports the synthesis of ferri-clinoholmquistite, nominally hLi2(Mg3Fe3+ 2)Si8O22(OH)2, at varying fO2 conditions. Amphibole compositions were characterized by X-ray (powder and single-crystal) diffraction, microchemical (EMPA) and spectroscopic (FTIR, Mo¨ ssbauer and Raman) techniques. Under reducing conditions (NNO+1, whereNNO=Nickel- Nickel oxide buffer), the amphibole yield is very high (>90%), but its composition, and in particular the FeO/ Fe2O3 ratio, departs significantly from the nominal one. Under oxidizing conditions ( NNO+1.5), the amphibole yield is much lower (

A well-characterized suite of vesuvianite samples from the volcanic ejecta of Latium (Italy) was studied by SREF (single-crystal X-ray refinement), EMPA, SIMS (Secondary-Ion Mass Spectrometry) and single-crystal, polarized radiation, FTIR spectroscopy in the OH-stretching region. Light elements in particular were analyzed by SIMS using an ion microprobe (Cameca IMS 4f) at CNR.-Istituto di Geoscienze e Georisorse (Pavia). A 16O- primary ion beam accelerated at 12.5 kV, with a beam intensity of 3 nA and a beam diameter

Synthetic NaNa2Mg5Si8O21(OH)3 is the fi rst triclinic member of the amphibole group, and has a tripling of the unit cell in the b direction. The space group is C1 . and the triple-b repeat gives Z = 6. The unit-cell parameters are: a = 9.883(2), b = 54.082(9), and c = 5.277(1) A, ?¿ = 90.045(4) 4?ÐF and for 4832 supercell refl ections in the 2?Æ range 2.25