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Spike (S) glycoprotein is the largest structural protein of SARS‐CoV‐2 virus and the main one involved in anchoring of the host receptor ACE2 through the receptor binding domain (RBD). S protein secondary structure is of great interest for shedding light on various aspects, from functionality to pathogenesis, finally to spectral fingerprint for the design of optical biosensors. In this paper, the secondary structure of SARS‐CoV‐2 S protein and its constituting components, namely RBD, S1 and S2 regions, are investigated at serological pH by measuring their amide I infrared absorption bands through Attenuated Total Reflection Infrared (ATR‐IR) spectroscopy. Experimental data in combination with MultiFOLD predictions, Define Secondary Structure of Proteins (DSSP) web server and Gravy value calculations, provide a comprehensive understanding of RBD, S1, S2, and S proteins in terms of their secondary structure content, conformational order, and interaction with the solvent. [ABSTRACT FROM AUTHOR]

Elucidating the high-temperature behavior of rock-forming minerals such as amphiboles (AB2C5 T8O22W2) is critical for the understanding of large-scale geological processes in the lithosphere and, in particular, the development of high conductivity in the Earth's interior. Recently, we have shown that at elevated temperatures, CFe-bearing amphiboles with a vacant A site develop two types of charge carriers: (1) small polarons and (2) delocalized H+ ions. To elucidate the effect of A-site cations on the formation and stability of charge carriers within the amphibole structure, here we analyzed synthetic potassic-ferro-richterite as a model Fe-rich amphibole with a fully occupied A site via in situ temperature-dependent Raman spectroscopy. We further compare the results from in situ time-dependent Raman-scattering experiments on pre-heated and rapidly quenched potassic-ferro-richterite and riebeckite as a model Fe-rich amphibole with a vacant A site. We show that the presence of A-site cations (1) reduces the activation temperature of mobile polarons and delocalized H+ cations; (2) decreases the magnitude of the polaron dipole moment; (3) slows down the process of re-localization of electrons on cooling; and (4) makes the electrons inert to rapid change in external conditions, supporting the persistence of a metastable state of pre-activated delocalized electrons even at room temperature. Our results have important geological implications demonstrating that the A-site cations may control the depth of development of high conductivity in subducted amphibole-bearing rocks. Moreover, from the viewpoint of mineral-inspired materials science, our results suggest that the amphibole-structure type has great potential for designing functional materials with tunable anisotropic-conductivity properties. [ABSTRACT FROM AUTHOR]

Microbial colonization can lead to various biodeterioration phenomena in outdoor stone monuments. To prevent these issues and mitigate the negative effects of chemical control, recent research has focused on encapsulating biocides in nanostructures. We tested the antifouling efficiency of the new multifunctional coating through in situ experiments performed on the Aurelian Walls in Rome. We selected two different biocides (2-mercaptobenzothiazole and zosteric sodium salt) and loaded them into two different silica nanocontainers (nanocapsules and mesoporous particles), which were dispersed in TEOS coatings. These coatings were applied to four common lithotypes (marble, travertine, mortar, and brick). Subsequently, we accelerated the colonization by inoculating microorganisms onto half of the samples, subjecting all samples to aging cycles. We conducted colorimetric, infrared spectroscopy, and other microscopic analyses to assess their durability and antimicrobial action. Our 3-year survey indicates that the coatings demonstrated antifoulant efficiency across all samples, with higher effectiveness observed on brick and mortar compared to travertine and marble. Among the nanostructures, nanocapsules exhibited greater efficiency than mesoporous particles, and regarding the biocides, the commercial one outperformed the natural one. These findings highlighted the potential of such systems in preserving cultural heritage; however, further research and product development is imperative for practical implementation. [ABSTRACT FROM AUTHOR]

All coronaviruses are characterized by spike glycoproteins whose S1 subunits contain the receptor binding domain (RBD). The RBD anchors the virus to the host cellular membrane to regulate the virus transmissibility and infectious process. Although the protein/receptor interaction mainly depends on the spike's conformation, particularly on its S1 unit, their secondary structures are poorly known. In this paper, the S1 conformation was investigated for MERS-CoV, SARS-CoV, and SARS-CoV-2 at serological pH by measuring their Amide I infrared absorption bands. The SARS-CoV-2 S1 secondary structure revealed a strong difference compared to those of MERS-CoV and SARS-CoV, with a significant presence of extended β-sheets. Furthermore, the conformation of the SARS-CoV-2 S1 showed a significant change by moving from serological pH to mild acidic and alkaline pH conditions. Both results suggest the capability of infrared spectroscopy to follow the secondary structure adaptation of the SARS-CoV-2 S1 to different environments. [ABSTRACT FROM AUTHOR]

This paper reports the occurrence and the crystal structure of fantappieite, a new member of the cancrinite-sodalite group of minerals from Torre Stracciacappe, Trevignano community (Rome, Latium, Italy). The mineral occurs within a volcanic ejectum consisting of dominant sanidine with minor plagioclase, biotite, augitic clinopyroxene, andradite, and iron oxides. Fantappieite (0.7 mm as largest size) is observed within miarolitic cavities of the rock as transparent colorless crystals, showing complex morphologies and striated faces. It is non-pleochroic and uniaxial negative, [n.sub.[omega]] = 1.5046(5) and [n.sub.[epsilon]] = 1.5027(5). [D.sub.calc] is 2.471 g/[cm.sup.3]. Fantappieite is trigonal, space group P[bar.3]; the cell parameters are: a = 12.8742(6), c = 87.215(3) [Angstrom], V= 12518.8(9) [[Angstrom].sup.3], Z= 1. The empirical chemical formula is: ([Na.sub.84.12][Ca.sub.30.00][K.sub.15.95][Fe.sub.0.19] [Ti.sub.0.13][Mn.sub.0.10][Mg.sub.0.09])([Si.sub.99.36] [Al.sub.98.64])[O.sub.396][(S[O.sub.4]).sub.30.24] [(C[O.sub.3]).sub.0.29][Cl.sub.0.84][F.sub.0.82]*5.18[H.sub.2]0, which corresponds to the ideal formula [[[Na.sub.82.5][Ca.sub.33] [K.sub.16.5].sub.[SIGMA]=132]([Si.sub.99][Al.sub.99] [0.sub.396])[(S[O.sub.4]).sub.33]*6[H.sub.2]0. The five strongest reflections in the X-ray powder pattern are [d in [Angstrom] (I %) (hkl)]: 3.70 (100) (3 0 0), 3.60 (80) (1 0 23), 2.641 (65) (0 0 33), 6.85 (60) (0 1 10), 6.40 (55) (1 1 0). The single-crystal FTIR spectrum rules out OH groups and shows the presence of [H.sub.2]O and CO2 molecules, as well. The structure can be described as a stacking sequence of 33 layers of six-membered rings of tetrahedra along the c axis. The stacking sequence is ACBACABACBACBACBCACBACBACBABCBACB ..., where A, B, and C represent the positions of the rings within the layers. This sequence gives rise to liottite, sodalite, and cancrinite cages, alternating along c. Sulfate groups occur within the liottite cages associated by Na, K, and Ca, while highly disordered sulfate groups are located within the sodalite cages. [H.sub.2]0 groups occur within the cancrinite cages, bonded to Ca and Na cations. Split positions are found for Na-Ca sites, and are related to disordering of the sulfate groups in the sodalite cages. Keywords: New minerals, fantappieite, crystal structure, IR spectroscopy, mechanical properties DOI: 10.2138/am.2010.3279

Eleven compositions along the join Na(NaMg)[Mg.sub.5][Si.sub.8][O.sub.22] [(OH).sub.2]-Na(NaCa)[Mg.sub.5][Si.sub.8][O.sub.22][(OH).sub.2] ('magnesiorichterite'-richterite) have been synthesized at T = 800-850[degrees]C and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. The run products have been characterized by electron probe microanalysis (EPMA), synchrotron and conventional X-ray powder diffraction (XRPD), Fourier transformed infrared (FTIR) spectroscopy, and selected area electron diffraction (SAED-TEM). Nominally, the chemical variation along the join can he expressed as [sup.B][Mg.sub.x.sup.B][Ca.sub.1-x] with 0 [less than or equal to] x [less than or equal to] 1. A combination of EPMA and FTIR data in the OH-stretching region show that a complete solid solution is obtained under the conditions used. Nevertheless, a slight deviation from the nominal compositions involving a limited loss of Na at A and B sites, balanced by an increase of Ca at the B site, is present. Several indications of a displacive and coelastic [P2.sub.1]/m [right arrow] C2/m transformation induced by the Ca-Mg chemical substitution are observed. The phase transition occurs at B-site composition ([X.sub.c]) close to [sup.B]([Na.sub.1][Mg.sub.0.7][Ca.sub.0.3]). C2/m samples with a Ca content of 0.34, 0.45, and 0.54 apfu show a significant strain tail related to local compositional inhomogeneities. This residual strain disappears as the amount of [sup.B]Ca significantly increases with respect to that of [sup.B]Mg. The transformation behavior observed here mirrors that of pyroxenes along the join diopside (CaMg[Si.sub.2][O.sub.6])-enstatite ([Mg.sub.2][Si.sub.2][O.sub.6]). The cell parameters of amphiboles with [sup.C][Mg.sub.5], [sup.T][Si.sub.8], and [sup.W][(OH).sub.2] and variable A- and B-site populations follow almost linear and continuous trends, indicative of small amounts of spontaneous strain accompanying these monoclinic phase transitions and the absence of significant miscibility gaps among different amphibole groups when quenched from higher temperatures of crystallization. Keywords: Synthetic amphiboles, XRPD, EPMA, SAED-TEM, FTIR spectroscopy, cell parameters, phase transition DOI: 10.2138/am.2010.3308

Human exposure to Volatile Organic Compounds (VOCs) and their presence in indoor and working environments is recognized as a serious health risk, causing impairments of varying severities. Different detecting systems able to monitor VOCs are available in the market; however, they have significant limitations for both sensitivity and chemical discrimination capability. During the last years we studied systematically the use of Fourier Transform Infrared (FTIR) spectroscopy as an alternative, powerful tool for quantifying VOCs in air. We calibrated the method for a set of compounds (styrene, acetone, ethanol and isopropanol) by using both laboratory and portable infrared spectrometers. The aim was to develop a new, and highly sensitive sensor system for VOCs monitoring. In this paper, we improved the setup performance, testing the feasibility of using a multipass cell with the aim of extending the sensitivity of our system down to the part per million (ppm) level. Considering that multipass cells are now also available for portable instruments, this study opens the road for the design of new high-resolution devices for environmental monitoring. [ABSTRACT FROM AUTHOR]

The thermal behavior of synthetic richterite [sup.A][Na.sup.B] [(NaCa).sup.C][Mg.sub.5.sup.T][Si.sub.8][O.sub.22][(OH).sub.2], crystallized at 800 [degrees]C and 0.35 GPa under hydrothermal conditions, was studied by serial powder diffraction experiments using synchrotron radiation between 123 and 873 K. The a, b, and [beta] cell parameters show a non-linear behavior, whereas the c parameter shows a linear trend; values of the saturation temperature [[theta].sub.s] are 410(3), 215(2), and 300(2) K for a, b, and asin[beta], respectively. The axial expansion pattern below room temperature is [[alpha].sub.b] > [[alpha].sub.c] > [[alpha].sub.a], whereas above room T it is [[alpha].sub.b] > [[alpha].sub.a] > [[alpha].sub.c], the difference being related to the different saturation temperatures of the individual cell parameters. The thermal expansion was modeled following the Debye approximation for the density-of-state of phonons; the refined parameters are [V.sub.0] = 908.20 (0.04) [[Angstrom].sup.3], k = 1 (4), [Q.sub.0] = 32 (2) MJ, and the Debye temperature [theta]D = 586(31) K. The non-linear behavior at low T is well described without systematic differences between the data and the model. The volume thermal expansion coefficient [[alpha].sub.v] changes significantly with temperature, also at temperatures higher than room temperature. It is suggested that this may occur also in other amphiboles and pyroxenes, requiring critical re-examination of the available data. A comparison of the strain tensor for the thermal expansion between amphiboles and pyroxenes shows that in amphiboles the major deformation occurs onto the (010) plane, whereas in pyroxenes it occurs along the b axis. Moreover, the major deformation on (010) in Ca-bearing pyroxenes occurs along the bond of the M2 cation with the furthermost O3 atoms, whereas in compositionally related Ca-amphiboles (i.e., tremolite) it occurs in a direction rotated by 10-20[degrees] to [a.sup.*], i.e., in a direction not corresponding to that of the M4-O5 bonds. It is proposed that the M4 polyhedron contributes less to the thermal deformation of amphibole than the M2 polyhedron contributes to the thermal deformation of pyroxene. Keywords: Richterite, amphibole, thermal expansion, Debye model, comparison with pyroxenes

This paper reports a single-crystal FTIR spectroscopic study of leucite, a nominally anhydrous mineral (NAM). Several transparent, inclusion-free samples from different occurrences and localities in the Alban Hills volcanic area (Latium, Italy) were analyzed. The FTIR spectra collected in the 4000-3000 [cm.sup.-1] [H.sup.2]O-stretching region show a broad absorption consisting of overlapping components at 3604, 3500, and 3245 [cm.sup.-1]. The occurrence of a well-defined combination band at 5225 [cm.sup.-1] indicates that almost all the examined samples contain hydrous components in the form of structurally bound water molecules. Using the integrated molar absorption coefficient from the working curve of Libowitzky and Rossman (1997), a water content up to >4000 ppm was obtained for the studied specimens. Detailed microspectroscopy mapping shows significant zoning of water in some samples, typically consisting of an anhydrous core mantled by a hydrous rim. The collected data suggest that careful study of the distribution of the volatile content of leucite (and associated volcanic NAMs) may provide a tool to monitor the evolution of the magmatic system where these minerals occur. Keywords: Leucite, Latium, single-crystal FTIR spectroscopy, microchemical composition, [H.sub.2]O mapping

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

This paper reports a single-crystal unpolarized-light FTIR study in the OH-stretching region of a suite of well-characterized Ti-rich pargasites from Lherz (French Pyrenees). All amphiboles studied have fairly constant M-site composition, with [sup.[6]][Al.sub.tot] ~0.55 atoms per formula unit (apfu), [sup.[6]]Ti ~0.45 apfu, and [sup.[6]][Fe.sup.3+] ~0.40 apfu. SIMS and SREF data show all samples to have an O3 anion composition of OH [approximately equal to] [O.sup.2-] [approximately equal to] 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.sup.-1], respectively, with an asymmetric tail extending to lower frequency. Six Gaussian components can be fitted to the spectra; comparison with spectra of both synthetic and natural pargasites allows five of these components to be assigned to local configurations involving OH-[O.sup.2-] at the O3 site, thus showing that coupling with an [O.sup.2-] anion through an A-cation significantly affects band position. Infrared spectroscopy can detect the presence of [O.sup.2-] in amphiboles in chemically favorable cases, i.e., in the absence of F. Moreover, the FTIR spectra show that all octahedral configurations involving [sup.M1][Ti.sup.4+] or [sup.M1][Fe.sup.3+] [sup.M3][Fe.sup.3+] are associated with [O.sup.2-] at both adjacent O3 sites, and that [sup.M3]Al is locally associated with OH, confirming SRO models based on structure refinement results. Keywords: Ti-rich pargasite, Lherz (French Pyrenees), single-crystal FTIR spectroscopy, anion occupancy

This paper reports a single-crystal FTIR spectroscopic study of vishnevite, ideally [[Na.sub.6](S[O.sub.4])][[Na.sub.2] [([H.sub.2]O).sub.2]]([Si.sub.6][Al.sub.6][O.sub.24]), a member of the cancrinite group of feldspathoids. The study was done on several crystals from various geological occurrences. Infrared spectra show that most samples, and in particular the specimens from the holotype locality at Vishnevye Mountains (Urals, Russia), contain molecular C[O.sub.2] as the main carbon species in the structural pores, while the specimens from Loch Borolan (Scotland) were found to be C[O.sub.3]-rich. Polarized-light measurements show that the linear C[O.sub.2] molecules are oriented perpendicular to the crystallographic c axis. Structure refinement of sample Pi4 from Latium (Italy) shows usual [H.sub.2]O *** Na *** [H.sub.2]O sequences within the undecahedral cages; however, difference Fourier maps suggest the presence of additional protons in the channels, possibly forming OH groups. The FTIR spectra show three absorptions in the 3800-3200 [cm.sup.-1] region. The first one, at 3590 [cm.sup.-1] is strongly polarized for E [perpendicular to] c while the second, at 3535 [cm.sup.-1], behaves almost isotropic. These two bands are assigned to the stretching vibrations of an asymmetric water molecule in the structural cages. The third broad absorption at 3320 [cm.sup.-1], is predominantly polarized for E||c and is assigned to additional OH groups in the channels. Detailed microspectroscopic mapping showed several samples from Latium (Italy) to be zoned with respect to the C[O.sub.2]/C[O.sub.3] content, thus pointing to a possible use of the volatile content of these minerals for petrological modeling. Keywords: Vishnevite, EMPA, crystal structure refinement, FTIR spectroscopy, channel molecules

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, [sup.A]Na [sup.B](CaMn) [sup.C][[Mg.sub.5][sup.T]([Si.sub.7]Al)[O.sub.22][(OH).sub.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 [sup.A][Na.sub.-1][sup.T][Al.sub.-1][sup.A][[??].sub.1][sup.T] [Si.sup.1] and [sup.B][Mn.sub.2][sup.B][Ca.sub.-2] exchange vectors. The first vector leads to parvo-manganotremolite, ideally [sup.A][??][sup.B] (CaMn)[sup.C][Mg.sub.5][sup.T][Si.sub.8][O.sub.22][(OH).sup.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., [sup.A] ([Na.sub.0.74][K.sub.0.02])[sup.B]([Ca.sub.1.27][Mn.sub.0.73])[sup.C] ([Mg.sub.4.51][Mn.sup.2+.sub.0.28][Fe.sup.2+.sub.0.05][Fe.sup.3+.sub.0.03] [Al.sub.0.12][Ti.sub.0.01])[sup.T]([Si.sub.7.07][Al.sub.0.93] [O.sub.22][(OH).sub.2], has a = 9.8260(5), b = 18.0487(9), c = 5.2840(4) [Angstrom], [beta] = 104.55(1)[degrees], V = 907.1 [Angstrom] (Z = 2); the calculated density is 3.11 g/[cm.sup.3]. The parvo-mangano tremolite crystal, with composition [sup.A]([Na.sub.0.44][K.sub.0.01])[sup.B]([Ca.sub.1.13] [Mn.sub.0.83][Na.sub.0.04][sup.C]([Mg.sub.4.69][Mn.sup.2+.sub.0.21] [Fe.sup.2+.sub.0.03][Fe.sup.3+.sub.0.01][Al.sub.0.06])[sup.T] ([Si.sub.7.52][Al.sub.0.48])[O.sub.22][(OH).sup.2], has a = 9.7807(5), b = 18.0548(9), c = 5.2928(4)[Angstrom], [beta] = [104.19(1)sup.o] V = 906.1 [[Angstrom].sup.3] 3 (Z = 2); the calculated density is 3.08 g/[cm.sup.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 FTIR spectrum of parvo-mangano-edenite in the OH-stretching region shows two main absorptions at 3711 and 3671 [cm.sup.-1], plus shoulders at 3695, 3660, and 3641 [cm.sup.-1], respectively. FTIR spectroscopy indicates extensive short-range-order of cations in these amphiboles. Keywords: Analysis, chemical (mineral), amphiboles, crystal structure, parvo-mangano-edenite, parvo-manganotremolite, IR spectroscopy, new minerals

This paper describes a high-pressure synchrotron infrared (IR) spectroscopy study of the synthetic amphibole Na(NaMg)[Mg.sub.5] [Si.sub.8][O.sub.22][(OH).sub.2]. This compound has P[2.sub.1]/m symmetry at room conditions; its IR OH-stretching spectrum consists of two main bands at 3743 and 3715 [cm.sup.-1], which are assigned to the two symmetrically independent O-H groups in the P structure (sample 403, Iezzi et al. 2004a). For increasing pressure, both bands shift toward higher frequency, suggesting a shortening of the O-H bond. In addition, the two bands progressively merge to give a single, symmetric and broad absorption band at 20-22 GPa. This behavior suggests that at 20-22 GPa there is a unique O-H group in the structure, indicative of a C-lattice type. The IR data thus show that the examined sample undergoes a P[2.sub.1]/m [left and right arrow], C2/m phase-transition at that pressure. Upon release of pressure, the initial two-band pattern is immediately recovered indicating that the pressure-induced phase-transition is reversible, as already observed for the same kind of transition induced by temperature. By analogy with structurally related pyroxenes, and taking into account the possible crystal structural topologies of amphiboles, we suggest that the C2/m polymorph stable at high pressure is characterized by fully kinked double-chains. Keywords: Amphibole, synthesis, IR spectroscopy, high-pressure, phase-transition

We describe here the synthesis of amphiboles along the nominal Na(NaMg) [Mg.sub.5][Si.sub.8][O.sub.22][(OH).sub.2]-Na(LiMg)[Mg.sub.5][Si.sub.8] [O.sub.22][(OH).sub.2] join, at 800 [degrees]C, 0.4 GPa. High amphibole yields (>90%) plus minor quartz and enstatite have been obtained at all compositions; amphibole crystals are acicular and their size rarely exceeds 20-30 x 0.5-3 [micro]m. TEM analysis shows the presence of h+k odd reflections in all samples, indicative of a P-lattice. By similarity with closely related amphiboles from the literature (e.g., Oberti et al. 2000; Camara et al. 2003) a P[2.sub.1]/m space group was assigned to the amphiboles synthesized here. Refined cell-parameters from X-ray powder-patterns show a linear decrease as a function of increasing Li at M4, a and [beta] being the most affected parameters. The four infrared OH-stretching spectra all show two main bands at 3741-3748 and 3712-3716 [cm.sup.-1], respectively. They are assigned to two independent O-H groups in the P[2.sub.1]/m structure, interacting with a strongly delocalized [sup.A]Na. The spectra show in addition two minor absorptions at about 3688 and 3667 [cm.sup.-1], respectively; these bands are assigned to vacant A-sites in the structure and indicate slight departure of the nominal composition toward cummingtonite. The present work shows that one apfu of [sup.B]Na can also be completely replaced by one apfu of [sup.B]Li ([M.sup.+]), in synthetic Na([M.sup.+]Mg)[Mg.sub.5][Si.sub.8][O.sub.22] [(OH).sub.2], and that all compositions have P[2.sub.1]/m symmetry at ambient conditions. Keywords: amphibole synthesis, FTIR spectroscopy, TEM, XRPD, amphibole symmetry

This paper reports the results of hydrothermal synthesis in the system [Na.sub.2]O-MgO-FeO-[Fe.sub.2][O.sub.3]-Si[O.sub.2][H.sub.2]O. Four samples of stoichiometric magnesioriebeckite composition, ideally [[][Na.sub.2][Mg.sub.3][Fe.sup.3+.sup.2][Si.sub.8] [O.sub.22](OH).sub.2], were run at 700-800 [degrees]C, 0.4 GPa, and redox conditions varying from NNO (Nickel-Nickel Oxide) to NNO + 2.3 log f[o.sub.2]. Powder XRD and SEM-EDX show a high (>85%) amphibole yield for all samples; however, in no case was the end-member composition attained. EMP analyses show that the amphiboles obtained deviate strongly from nominal stoichiometry toward magnesio-arfvedsonite [[Na[Na.sub.2][Mg.sub.4][Fe.sup.3+][Si.sub.8][O.sub.22](OH).sub.2]]. Powder XRD patterns were indexed in the space group C2/m; refined cell-parameters reflect variations in the amphibole composition, and the cell volume is correlated linearly with the A-site occupancy. Mossbauer spectra show that in all samples, [Fe.sup.3+] is completely ordered at M2, whereas [Fe.sup.2+] occurs at the M1, M3, and M4 sites. The [Fe.sup.3+]/[Fe.sup.2+] ratio is a function of f[o.sub.2]: for increasing oxidation conditions, there is significant increase in [sup.M2][Fe.sup.3+] and decrease in [Fe.sup.2+], notably in [sup.M4][Fe.sup.2+]. Mossbauer spectra also show significant variation in [sup.M1][Fe.sup.2+] and [sup.M3][Fe.sup.2+] quadrupole splitting as a function of the [Fe.sup.3+] content in the amphibole. IR spectra in the OH-stretching region show a well-resolved quadruplet at frequencies

Synthetic Na[Na.sub.2][Mg.sub.5][Si.sub.8][O.sub.21][(OH).sub.3] is the first triclinic member of the amphibole group, and has a tripling of the unit cell in the b direction. The space group is C[bar.1] 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) [Angstrom], [alpha] = 90.045(4)[degrees], [beta] = 103.068(3)[degrees] [gamma] = 89.960(4)[degrees], and V = 2748(1) [[Angstrom].sup.3]. The crystal structure has been refined to [R.sub.1] = 7.6 and w[R.sub.2] = 16.7% for the 1835 reflections with [F.sub.o] > 4[[sigma].sub.F] and for 4832 supercell reflections in the 2[theta] range 2-25[degrees], respectively. The structure is pseudo-monoclinic, but both the intensity distribution and refined model indicate space group C[bar.1]. Compared with the common C2/m amphibole structure, the two halves of an I-beam unit are no longer mirror-related, and the overall structure can be rationalized in terms of two different types of I-beam occurring in the unit cell. The first (with multiplicity 2) is centrosymmetric, and the second (with multiplicity 4) is non-centrosymmetric. There are also significant displacements of the cations, especially at the M4 sites, from their corresponding locations in the C2/m structure. The correlated displacements of Na atoms at the M4 sites permit incorporation of excess protons in pseudo-tetrahedral cavities between two adjacent chains of tetrahedra belonging to different I-beams. Bond-valence calculations and crystal-chemical analysis suggest that excess protons are bonded to O atoms at the O4 sites, and are hydrogen bonded to O atoms at adjacent O2 sites. The infrared spectrum of the amphibole in the principal OH-stretching region has a triplet of sharp bands at 3740, 3727, and 3711 [cm.sup.-1], which are assigned to the three independent 'normal' O3-H groups in the triclinic structure. There is an additional intense and very broad absorption at 3430 [cm.sup.-1] that is resolved only when adsorbed moisture is removed. This band is assigned to the extra H in the structure. All the details provided by structure refinement and the proposed location of the excess H atoms is in accord with previous HRTEM and [sup.29]Si- and [sup.1]H MAS NMR studies of this amphibole.

In the present work, we characterize the amphibole Na(NaMg)[Mg.sub.5][Si.sub.8][O.sub.22][(OH).sub.2] synthesized at 0.4 GPa and 750, 800, and 850 [degrees]C, and 0.5 GPa, 900 [degrees]C. Experiments at 800 and 900 [degrees]C yielded crystals suitable for single-crystal data collection. Structure refinement shows that synthetic Na(NaMg)[Mg.sub.5][Si.sub.8][O.sub.22][(OH).sub.2] has P[2.sub.1]/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)[Mg.sub.5][Si.sub.8][O.sub.22][(OH).sub.2] has two well-defined absorption bands at 3742 and 3715 [cm.sup.-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 tYequency band is assigned to the longer O3A-H1 bond. The broader shape of the 3743 [cm.sup.-1] band is consistent with a stronger interaction of the H2 atom with [sup.A]Na, which is confirmed by structure refinement. Increasing Tof synthesis causes a progressive departure from the ideal stoichiometry via the A[[cube root of].sub.1][sup.B][Mg.sub.1][sup.A][Na.sub.-1][sup.B][Na.sub.-1] substitution, as confirmed by EMPA, structure refinement, and FFIR spectroscopy.

Amphiboles were hydrothermally synthesized at 500[degrees]C and 4 kbar in the system [Li.sub.2]O-[Na.sub.2]O-FeO-[Fe.sub.2] [O.sub.3]-Si[O.sub.2]-[H.sub.2]O, with nominal compositions along the riebeckite [[][Na.sub.2][Fe.sup.2+.sub.3][Fe.sup.3+.sub.2]+[Si.sub.8] [O.sub.22] ([OH).sub.2]]-ferri-clinoferroholmquistite [[][Li.sub.2] [Fe.sup.2+.sub.3][Fe.sup.3.sub.2]+[Si.sub.8][O.sub.22]([OH).sub.2]] join, where the exchange vector is Na[Li.sub.-1] at the B-site. Experimental products were characterized by powder XRD and SEM-EDAX, confirming very high amphibole yield along the join (>95%, plus minor quartz). The XRD patterns can be indexed in C2/m, and the refined cell parameters show linear variation as a function of composition. For the [sup.B]Li end-member, the IR spectrum shows a single sharp main band centered at 3614 [cm.sup.-1], which is assigned to the FeFeFe-O[H-.sup.A][] configuration. With increasing [sup.B]Na in the mineral, this band broadens and shifts 4 [cm.sup.-1] to higher frequencies. This effect can be attributed to the change in M4 site occupancy. Minor [sup.A]Na (partial solid-solution toward arfvedsonite) is also observed with increasing sodium in the system. Mossbauer spectroscopy confirms the cation distribution provided by IR data, and shows that a small, but significant amount of [Fe.sup.2+] occurs at M4 along the join. Infrared spectroscopy shows that the Li end-member has a very ordered structure, whereas intermediate compositions show local heterogeneities associated with the presence of two different B sites occupied by Na or Li.

Detailed X-ray single-crystal structure refinements and complete (SIMS + EMPA) microprobe chemical analyses of a series of non-metamict samples of hellandite recently found in Latium (Italy), together with a critical re-evaluation of the existing data on hellandite, allow a better understanding of the crystal-chemistry of the hellandite group. Relative to the crystal structure determined by Mellini and Merlino (1977) for a Y-rich sample from Predazzo (Italy), a new tetrahedrally coordinated site has been detected; this may be fully, or in part, occupied by Li and Be. These cations occur at the center of the tetrahedral cavity where the H atom, which is bonded to the O5 O atom, protrudes; thus the H content in hellandite is constrained to values [less than or equal to] 2 - (Li + Be + F). A new general formula for hellandite-group minerals is proposed: [X.sub.4][Y.sub.2]Z[T.sub.2][[B.sub.4][Si.sub.4][O.sub.22]][W.sub.2], where X = Na, Ca, Y, LRE[E.sup.3+] at the eightfold-coordinated M3 and M4 sites; Y = Ca, Y, HRE[E.sup.3+], [Th.sup.4+ at the eightfold-coordinated M2 site; Z = Al, [Mn.sup.3+], [Fe.sup.3+], [Ti.sup.4+] at the octahedral M1 site; T = [square] (vacancy), Li, Be at the new tetrahedrally coordinated site; and W = OH, F, [O.sup.2-] at the 05 site. Eight root end-member compositions were identified; four of these correspond to known compositions: hellandite-(REE), tadzhikite-(REE), and two new minerals, mottanaite-(Ce) and ciprianiite, which are described in a companion paper (Della Ventura et al. 2002). The root-name tadzhikite must be used for samples with [Ti.sup.4+] > 0.5 apfu, with no reference to the OH content. Hellandite is an REE mineral. Rare-earth elements occur at two distinct sites (M2 and M4), with a strong preference for M2 (particularly HREE). Thus, one or two Levinson modifiers can be added to the root name to correctly describe the species. A sequence of incorporation based on crystalchemical arguments is provided and allows evaluation of the site populations for nomenclature purposes. This redefinition of the hellandite group and the new nomenclature rules have been approved by the IMA Commission on New Minerals and Mineral names (code 00-F).

Two new minerals of the hellandite group were found within alkali-syenitic ejecta enclosed in pyroclastic formations of the Roman Comagmatic Province (Latium, Italy). Mottanaite-(Ce) [ideally [sup.X][Ca.sup.Y.sub.4][(CeCa).sup.Z][Al.sup.T][Be.sub.2] [([Si.sub.4][B.sub.4][O.sub.22]).sup.W][O.sub.2]] and ciprianiite [ideally [sup.X][Ca.sup.Y.sub.4][[(Th,U)(REE)].sup.Z][Al.sup.T][[square].sub.2] ([Si.sub.4][B.sub.4][O.sub.22]) [sup.W][(OH, F).sub.2]] occur as transparent, brown-colored, tabular euhedral crystals in miarolitic cavities and voids of the ejecta, which consist mainly of sanidine and plagioclase (An ranging from 20 to 80%), with minor amounts of feldspathoid, clinopyroxene and/or clinoamphibole, magnetite, titanite, and zircon. Locally, accessory minerals include britholite-(Ce), baddeleyite, phosphate to silico-phosphate phases close in composition to the brabantite-cheralite series, thorite, fluorite, danburite, and vonsenite. The genesis of the new hellandite end-members can be related to late-stage post magmatic hydrothermal fluids enriched in Zr, Ti, REEs, and actinide elements. Both mottanaite-(Ce) and ciprianiite have a vitreous luster and are non-fluorescent. Cleavage is absent in mottanaite-(Ce), fair to good in ciprianiite, {100}. Twinning is frequently observed in ciprianiite. Due to the strong intra-crystalline chemical zoning and twinning, physical properties could be measured only for mottanaite-(Ce). [D.sub.meas] is 3.61(4) g/[cm.sup.3], [D.sub.calc] is 3.88 g/[cm.sup.3]. Mottanaite-(Ce) is biaxial negative, with [alpha] = 1.680(5), [beta] = 1.694(2), [gamma] = 1.708(5); 2[V.sub.meas] ~90 [degrees]. Both minerals are monoclinic, space group P2/a, Z = 2. Unit-cell parameters for the crystals studied are: a = 19.032(9) [Angstrom], b = 4.746(3) [Angstrom], c = 10.248(5) [Angstrom], [beta] = 110.97(5) [degrees], V = 864.3(8) [[Angstrom].sup.3] for mottanaite-(Ce), and a = 19.059(5) [Angstrom], b = 4.729(1) [Angstrom], c = 10.291(4) [Angstrom], [beta] = 111.33(2) [degrees], V = 864.0(5) [[Angstrom].sup.3] for ciprianiite. Single-crystal structure refinement confirmed the presence of a further distorted tetrahedral site which was first detected in a hellandite-(Ce) sample from Latium (Oberti et al. 1999). This site is occupied by Be ([+ or -] Li) in stoichiometric mottanaite-(REE), whereas it mainly hosts hydrogen (bonded to the 05 oxygen atom) in ciprianiite and hellandite-(REE); solid solution between the end-members is possible, as shown by the studied samples. The chemical composition of the refined crystals was obtained by combining EMPA (for medium-Z elements) and SIMS analyses (for low- and high-Z elements); their results are in excellent agreement with the chemical information obtained from the structure refinements. The crystal-chemical formulae of the crystals studied, recalculated on the basis of 24 anions, are [sup.M3,4][Ca.sup.M2.sub.4] [[RE[E.sub.1.45][Ca.sub.0.37][(Th,U).sup.4+.sub.0.17] [Y.sub.0.01]].sub.[SIGMA]=2][sup.M1][([Al.sub.0.50] [Fe.sup.3+.sub.038][Mg.sub.0.03] [Ti.sup.4+.sub.0.07]).sub.[SIGMA]=0.99][sup.T] ([Be.sub.1.18][Li.sub.0.02][[square].sub.0.37]) [B.sub.3.99][Si.sub.3.98][O.sub.22][sup.O5][([O.sup.2-.sub.1.04] [F.sub.0.53]O[H.sub.0.43]).sub.[SIGMA]=2] for mottanaite-(Ce); and [sup.M3,4][Ca.sub.4][sup.M2][[RE[E.sup.3+.sub.0.72] [(Th,U).sup.4+.sub.0.66][Ca.sub.0.60][Y.sub.0.02]].sub.[SIGMA]=2] [sup.M1][([Al.sub.0.48][Fe.sup.3+.sub.0.38][Ti.sup.4+.sub.0.10][Mg.sub.0.05] [Mn.sup.3+.sub.0.02]).sub.[SIGMA]=1.03][sup.T] ([Be.sub.0.82][[square].sub.0.60][Li.sub.0.04]) [B.sub.4.00][Si.sub.4.00][O.sub.22][sup.O5][([O.sup.2-.sub.0.97]O [H.sub.0.54][F.sub.0.49]).sub.[SIGMA]=2] for ciprianiite.