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kircherite (IMA 2009-084), a new member of the cancrinitesodalite group of minerals from Valle Biachella, Sacrofano, (Rome), in the Sabatini volcanic complex, Latium, Italy. The mineral occurs within miarolitic cavities of holocrystalline, syenitic, volcanic ejecta, associated with sodalite, biotite, iron oxides, titanite, fluorite, and a pyrochlore group mineral. The groundmass of the ejecta consists essentially of potasiumfeldspar, with minor sodalite and brown mica. Kircherite occurs typically as parallel associations of hexagonal, thin, tabular crystals (2 or 3 mm in diameter and 1 mm in thickness). Single platelets have a thickness that very rarely exceeds 0.5 mm. Crystals are colourless to light gray to white, translucent to opaque in the most altered parts of the crystals; lustre is greasy to silky. Fluorescence is in light pink under LW UV and deep red under SW UV. Hardness is (Mohs): 5.5; micro-indentation VHN load 10 g, mean 648.4 kg mm-2, range ± 208.9 kg mm-2. Cleavage on {001} is good. Density (calc.) is 2.457 g cm-3. Kircherite is non-pleochroic and uniaxial negative with ω = 1.510(2), ε = 1.502(2). Kircherite is trigonal, space group R32, with , a = 12.8770(7) Å, c = 95.224(6) Å, V = 13677.2(13) Å3, Z = 1. The empirical chemical formula obtained from EMP analyses is: (Na89.09Ca31.63K18.85Fe0.20Mn0.06Mg0.05Ti0.03)Σ=139.91 (Si108.13 Al107.87)Σ=216.00O430.08(SO4)32.59 Cl2.00F0.53(CO3)0.09·6.86H2O, which corresponds to the ideal formula [Na90Ca36K18]Σ=144 (Si108Al108O432)(SO4)36·6H2O. The strongest six reflections in the X-ray powder pattern are [d in Å (I %) (hkl)]: 3.72 (100) (300), 2.65 (100) (2.1.28; 0.0.36), 3.23 (65) (2.1.19), 3.58 (60) (1.2.14), 3.60 (53) (1.0.25), 3.80 (52) (1.2.11). The single-crystal FTIR spectrum rules out OH groups and shows the presence of H2O and CO2 molecules in the structural cages of the mineral. The structure can be described as a stacking sequence of 36 layers of six-membered rings of tetrahedra along the c axis as ACABCABCABCACBCABCABCABCBABCABCABCAB…, where A, B and C represent the positions of the rings within the layers. The structure has 6 cancrinite cagϵe)s, 2(4 sodalite cages (S) and 6 LOSOD cages (L) within the unit cell, and these account for a maximum of 36 SO4 2- groups and 6 H2O molecules (or Cl anions). There is a unique sequence of cages, ϵSSSLSSLSSSϵ and adjacent sequences are shifted 1/3 along [001]. Kircherite, having 36 layers, is the cancrinite with the longest complex sequence described to date. The name is for Athanasius Kircher (1602–1680), a German Jesuit who was the founder of the museum of the Collegium Romanum in 1651, hereafter named the Museum Kircherianum.

Extensive spectroscopic, diffraction and theoretical work in the last ten years has shown that short-range order (SRO) of both cations and anions is a common feature of amphiboles (Hawthorne et al. 2005). From an experimental perspective, the problem is that SRO does not obey the translational symmetry of the structure in which it occurs, and hence SRO is diffi cult to detect and decipher directly by standard diffraction methods. There is information on SRO resident in diffuse scattering from a crystal, but this information is quite diffi cult to extract, particularly when the SRO is complicated, and this approach has only been used for simpler materials. SRO can be detected by several spectroscopic techniques [e.g., infrared spectroscopy, magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy], but the problem is that only part of the local arrangement is derived, and the complete picture of SRO is often not clear. Here, we examine SRO of cations and anions in monoclinic amphiboles, and show that detailed information on SRO can be derived by a combination of infrared spectroscopy and local bond-valence theory, augmented by results from Rietveld and single-crystal diffraction.

In this chapter, we examine the new amphibole compositions which have been found and characterized since 1981, i.e. since the publication of volume 9A of the MSA Reviews in Mineralogy. We divide the chapter in two sections. The fi rst section describes new charge arrangements found in Nature, and the second section describes the extensive studies of synthetic amphiboles of novel composition done to clarify the crystal chemistry of exotic cations which are normally found as minor components. This chapter deals exclusively with monoclinic amphiboles, as the compositional space of orthorhombic amphiboles has not expanded since the former review. Although natural occurrences of protoamphibole (with space group Pnmn) have been described only in the last twenty years (Sueno et al. 1998; Konishi et al. 2003), their composition is within the compositional range previously defi ned for Pnma amphiboles.

High-temperature Fourier transform infrared (HT-FTIR) spectroscopy was used to characterize the deprotonation process of synthetic potassic-ferro-richterite of composition A ( K 0 . 90 Na 0 . 07 ) B ( Ca 0 . 54 Na 1 . 46 ) C ( Fe 4 . 22 2 + Fe 0 . 78 3 + ) T Si 8 O 22 W ( OH 1 . 70 O 0 . 30 2 − ) . Unpolarized single-crystal spectra were collected both in situ and on quenched samples, and heating experiments were conducted in air, at a rate of 10 °C/min. The room- T spectrum measured before annealing shows a main band at 3678 cm −1 and a minor band at 3622 cm −1 ; these are assigned to local configurations involving Fe 2+ at M (1) M (1) M (3) and facing a filled and an empty alkali-site, respectively. At 400 °C, a new band grows at 3656 cm −1 ; this is the most intense feature in the pattern at 450 °C. At T ≥ 500 °C, all peaks decrease drastically in intensity, and finally disappear at T > 600 °C. The total absorbance measured in situ increases significantly in the 25 T T range. This feature is consistent with an increase of the absorption coefficient (e) with T , the reason for which is still unclear. However, this feature has significant implications for the quantitative use of FTIR data in HT experiments. Examination of the relevant OH-stretching bands shows that iron oxidation occurs preferentially at the M (1,3) sites associated with occupied A sites. The deprotonation temperature indicated by FTIR for single-crystals is around 100 °C higher that that obtained by HT-X-ray diffraction (XRD) on single crystal by Oberti et al. (2016), whereas that obtained by HT-XRD on powders is intermediate. This unexpected observation can be explained by considering that: (1) the iron oxidation process, which is coupled to deprotonation and is probed by XRD, occurs preferentially at the crystal surface where it is triggered by the availability of atmospheric oxygen; (2) the proton diffusion, probed by FTIR, is slower that the electron diffusion probed by XRD; thus, the temperature shift may be explained by a much longer escape path for H in single-crystals than in powders. These results suggest that possible effects due to crystals size should be carefully considered in HT experiments done on Fe-rich silicates.

This paper reports on the occurrence and the crystal structure of kircherite, a new member of the cancrinite-sodalite group of minerals from Valle Biachella, Sacrofano community (Rome, Latium, Italy). The mineral occurs in association with sodalite, biotite, iron oxides, titanite, fluorite, and a pyrochlore-group mineral. The groundmass of the ejectum consists essentially of K-feldspar with subordinate plagioclase. Kircherite (3 mm as largest size) is observed within miarolitic cavities of the rock and typically occurs as parallel associations of hexagonal, thin, tabular colorless to light-gray transparent crystals; it is non-pleochroic and uniaxial negative, with ω = 1.510(2) and ɛ = 1.502(2). D calc is 2.457 g/cm 3 . Kircherite is trigonal with a = 12.8770(7), c = 95.244(6) A, V = 13677(1) A 3 , Z = 1. The structure has been refined in the trigonal space group R 32, obtaining a R -value of 8.5% on 8131 reflections with I /σ I > 2. The strongest seven reflections in the X-ray powder pattern are [ d in A (I %) ( hkl )]: 3.717 (100) (3 0 0), 2.648 (100) (2 1 28; 0 0 36), 3.232 (65) (2 1 19), 3.584 (60) (1 2 14), 3.604 (53) (1 0 25), 3.799 (52) (1 2 11), 3.220 (38) (2 2 0). The single-crystal FTIR spectrum rules out OH groups and shows the presence of H 2 O and CO 2 molecules in the structural cages of the mineral. Chemical analysis gives (in wt%): SiO 2 32.05, Al 2 O 3 27.13, FeO 0.07, K 2 O 4.38, CaO 8.75, Na 2 O 13.62, MgO 0.01, MnO 0.02, TiO 2 0.01, SO 3 12.87, Cl 0.35, F 0.05, total 99.82. The empirical formula calculated on the basis of ∑(Si+Al) = 216 apfu is (Na 89.09 Ca 31.63 K 18.85 Fe 0.20 Mn 0.06 Mg 0.05 Ti 0.03 ) ∑=139.91 [(Si 108.13 Al 107.87 ) ∑=216.00 O 430.00 ](SO 4 ) 32.58 Cl 2.00 F 0.53 ·6.86H 2 O, which corresponds to the ideal formula [Na 90 Ca 36 K 18 ] ∑=144 (Si 108 Al 108 O 432 )(SO 4 ) 36 ·6H 2 O. The structure can be described as a stacking sequence of 36 layers of six-membered rings of tetrahedra along the c axis. The stacking sequence is ACABCABCABCACBCABCABCABCBABCABCABCAB…, where A, B, and C represent the positions of the rings within the layers. This sequence gives rise to cancrinite, sodalite, and losod cages, alternating along c . Sulfate groups occur within the sodalite and losod cages associated by Na, K, and Ca. H 2 O groups occur within the cancrinite cages, bonded to Ca and Na cations. Anion groups (SO 4 2− ) in sodalite cages show positional disorder, and so do consequently the extraframework cation sites related to them.

Eleven compositions along the join Na(NaMg)Mg(5)Si(delta)O(22)(OH)(2)-Na(NaCa)Mg(5)Si(8)O(22)(OH)(2) ("magnesiorichterite"-richterite) have been synthesized at T= 800-850 degrees C and P(H2O) = 0.35-0.5 GPa. 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 call be expressed as (B)Mg(x)(B)Ca(1-x) with 0 C2/m transformation induced by the Ca-Mg chemical Substitution are observed. The phase transition Occurs at B-site composition (X(c)) close to (B)(Na(1)Mg(0.7)Ca(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 Lis the amount of (B)Ca significantly increases with respect to that of (B)Mg. The transformation behavior observed here mirrors that of pyroxenes along the join diopside (CaMgSi(2)O(6))-enstatite (Mg(2)Si(2)O(6))- The Cell parameters of amphiboies with (C)Mg(5), (T)Si(8), and (W)(OH)(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.

The crystal structure and crystal chemistry of two natural pollucite samples, from Buckfield, Oxford County, Maine (sample M3), and from Kanzit Mawaie, Laghman, Nooristan, Afghanistan (sample N5), have been investigated by means of wavelength-dispersive X-ray microanalysis, thermogravimetric analysis, single-crystal X-ray and neutron diffraction, and single-crystal Fourier-transform infrared spectroscopy. The X-ray and neutron diffraction patterns of the two pollucite crystals show a metrically cubic unit cell [with a(M3) = 13.6914(6) angstrom and a(N5) = 13.6808(6) angstrom by neutron diffraction data; the deviation from isometry is 4 sigma(F(o)) for M3 and R(1) = 0.0693 for 31 refined parameters and 331 unique reflections with F(o) > 4 sigma(F(o)) for N5. The structure refinements show a disordered Si/Al-distribution in the tetrahedral framework. The analysis of the difference-Fourier maps of the nuclear density confirms the presence of extra-framework water molecules with oxygen sharing the Cs site (at 1/8, 1/8, 1/8, Wyckoff-16b position). However, the minima, ascribable to the proton sites, are very weak in density. Two possible proton positions, leading to a reasonable H(2)O configuration, are given, and the possible hydrogen bonding is described. Sodium is located at 1/4, 1/8, 0 (Wyckoff-24c position). The main IR absorption bands in the regions typical of H(2)O are assigned, and the presence of hydroxyls in the studied samples is ruled out. Neutron diffraction and FTIR data agree with the presence of very weak hydrogen bonds in the structure. The detailed description of the crystal structure and crystal chemistry of pollucite (e.g., Si/Al-distribution, configuration of the extra-framework content, possible hydrogen bonding scheme) reported in this study is the key to understand the high thermo-elastic stability of pollucite, the immobility of Cs at non-ambient conditions, and the extremely low leaching rate of Cs, which make this open-framework silicate a promising material with potential use for fixation and deposition of Cs radioisotopes.

The thermal behavior of synthetic richterite Na-A(B)(NaCa)(Mg5Si8O22)-Mg-C-Si-T(OH)(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(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(b) > alpha(c) > alpha(a), whereas above room T it is alpha(b) > alpha(a) > alpha(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-0 = 908.20 (0.04) angstrom(3), k = 1 (4), Q(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(F) 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*, 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.

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(3) was refined in the P2(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 (Ca0.81REE0.66Y0.39Th0.13U0.02)(Sigma 2.01)(Fe0.292+Li0.14 Fe0.123+Mn0.02Mg0.01)(Sigma 0.58)(Si1.98Be1.09B0.81Li0.12)(Sigma 4.00) O-8(O1.20F0.51OH0.29)(Sigma 2.00,) which yields a calculated density of 4.267 g cm(-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) Fe-x(2+) + Y-A -> Li-x + (A)(Th + U) and (2) Be-z + Fe-x(2+) -> Li-z + Fe-x(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.

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 Al-[6](tot) similar to 0.55 atoms per formula unit (apfia), Ti-[6] similar to 0.45 apfia, and Fe-[6](3+) similar to 0.40 apfu. SIMS and SREF data show all samples to have an 03 anion composition of OH approximate to O2- approximate 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: similar to 3710, 3686, and 3660 cm(-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-2- at the 03 site, thus showing that coupling with an O2- anion through an A-cation significantly 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 configurations involving Ti-M1(4+) or Fe-M1(3+) Fe-M3(3+) are associated with O2- at both adjacent 03 sites, and that Al-M3 is focally associated with OH, confirming SRO models based on structure refinement results.

This paper reports a single-crystal FTIR spectroscopic study of vishnevite, ideally [Na-6(SO4)] [Na-2(H2O)(2)](Si6Al6O24), 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 CO2 as the main carbon species in the structural pores, while the specimens from Loch Borolan (Scotland) were found to be CO3-rich. Polarized-light measurements show that the linear CO2 molecules are oriented perpendicular to the crystallographic c axis. Structure refinement of sample Pi4 from Latium (Italy) shows usual H2O center dot center dot center dot Na center dot center dot center dot H2O 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(-1) region. The first one, at 3590 cm(-1) is strongly polarized for E perpendicular to c while the second, at 3535 cm(-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(-1), is predominantly polarized for E vertical bar vertical bar 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 CO2/CO3 content, thus pointing to a possible use of the volatile content of these minerals for petrological modeling.

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 P21/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 P21/m {leftrightarrow} 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.

We describe here the synthesis of amphiboles along the nominal Na(NaMg)Mg 5 Si 8 O 22 (OH) 2 −Na(LiMg)Mg 5 Si 8 O 22 (OH) 2 join, at 800 °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 × 0.5–3 μm. 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 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 β being the most affected parameters. The four infrared OH-stretching spectra all show two main bands at 3741–3748 and 3712–3716 cm −1 , respectively. They are assigned to two independent O-H groups in the P 2 1 / m structure, interacting with a strongly delocalized A Na. The spectra show in addition two minor absorptions at about 3688 and 3667 cm −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 B Na can also be completely replaced by one apfu of B Li (M + ), in synthetic Na(M+Mg)Mg 5 Si 8 O 22 (OH) 2 , and that all compositions have P 2 1 / m symmetry at ambient conditions.

The crystal structure of a Th-U-rich, Y-poor hellandite-(Ce) occurring in a volcanic ejectum from Capranica (Vico volcanic complex, Latium, Italy) was refined to an R index of 1.5% for 2226 observed reflections [I > 3 sigma(I)]. Hellandite from Capranica is monoclinic P2/a with a = 19.068 (8), b = 4.745 (2), c = 10.289 (3) Angstrom, beta = 111.18 (3)degrees. The extra-framework (distorted) tetrahedral cavity, usually occupied by H in hellandite, is partially (35-40%) occupied by Be and/or Li. When this is the case, the [B4Si4O22] tetrahedral chains of hellandite are locally cross-linked to form a sheet, which is built up by the same types of rings as in semenovite but in a different arrangement. The structure refinement and the electron- and ion-microprobe analyses provide constraints on hellandite-group crystal chemistry. The presence of ([4])(Be, Li) at the Be site is coupled with the substitution of F and/or O for OH at the O5 site; the amount of extra-framework cations thus constrains the OH content in the general formula. X-ray data exclude the presence of other OH sites in the structure, in agreement with direct H determination by ion probe (1.02 H apfu + 0.98 F apfu = 2.0 apfu of monovalent anions at O5 vs. 4.5-8 apfu proposed previously). The complete chemical analysis also eliminates the need for a vacancy at the REE sites. The general formula of hellandite-group minerals is thus (Ca,REE)(8)(Th,U,Y,REE)(4)(Ti,Fe3+,Al)(2)(O,F,OHx)(4)(Be,Li)(4-x)Si8B8O44, where electroneutrality is assured by the appropriate mixing of heterovalent substituents at the M sites.