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The crystal structure and chemical composition of boussingaultite from Pécs-Vasas, Mecsek Mountains, South Hungary, were investigated by single-crystal neutron diffraction (at 20 K) along with a series of chemical analytical techniques [i.e., gravimetric determination of sulfates, EDTA titrimetric determination of magnesium, ion selective electrode for F and Cl, indirect gravimetric determination of ammonium as (NH4,Rb,Cs,K) tetraphenylborate, inductively coupled plasma atomic emission spectroscopy for REE and other minor elements, elemental analysis for C, N, and H content, high-T mass loss for H2O content]. The concentrations of more than 50 elements were measured. The experimental formula of the boussingaultite is: [(NH4)1.77K0.22)Σ1.99[(Mg0.95Mn0.06)Σ1.01(H2O)5.7](SO4)1.99. Neutron data analysis confirms that the structure of boussingaultite is built up by isolated Mg(H2O)6- octahedra, along with isolated NH4- and SO4-tetrahedra connected by a complex H-bonds network. Mg2+ is completely solvated by H2O molecules in a typical octahedral bonding configuration. All the seven independent oxygen sites in the structure are involved in H-bonds, as donors or as acceptors. The geometry of all the H2O molecules, bonded to Mg, is in line with that usually observed in crystalline compounds. The H2O molecules show moderate-strong H-bonds, with H···Oacceptor and Odonor···Oacceptor ranging between 1.72–1.87 and 2.70–2.84 Å, respectively, along with Odonor-H···Oacceptor angles between 168–178°. The four independent N-H···O bonds show H···Oacceptor and Ndonor···Oacceptor distances ranging between 1.81–2.00 and 2.84–2.98 Å, respectively, with N-H···O angles between 158–176°. All the H-bonds of the H2O molecules and of the NH4-group involve the oxygen sites of the SO4-group as acceptors: the SO4-group is, therefore, the "bridging unit" between the NH4 and the Mg(H2O)6 units, via H-bonds. Our structure refinement proved, unambiguously, that the partial K4+ vs. NH+ replacement generates a local disorder. K lies at the N site, and its bonding configuration can be described by a distorted polyhedron with CN = 8. However, the K+ vs. NH+ replacement implies 4 a change in the configuration of the SO4- tetrahedron, through a sort of rotation of the polyhedron. This is the first evidence of the presence of a partial picromerite component in the boussingaultite structure, which gives rise to a local disorder likely due to the significantly different bonding configurations of the two cations. Our refinement also revealed that Mn2+ replaces Mg2+ at the Mg site. No evidence of distortion of the octahedron is observed in response to such a replacement, but the fraction of Mn2+ is modest. An analysis of previous Raman and IR results is provided, and is compared with the experimental results of this study. [ABSTRACT FROM AUTHOR]

An As-rich variety of fergusonite-beta-(Y) occurs as greenish yellow pseudo-bipyramidal crystals up to 1 mm in length in centimeter-sized secondary cavities within sub-horizontal pegmatite dikes at Mount Cervandone (Western Alps, Italy). The mineral is associated with quartz, biotite, potassium feldspar, and orange-yellow barrel-shaped hexagonal crystals of synchysite-(Ce) up to 2 mm in length. Fergusonite-beta-(Y) crystallized during the Alpine metamorphism under amphibolite-facies conditions, as a result of interaction between As-enriched hydrothermal fluids, circulating through the pegmatite dikes, and precursor accessory minerals in the pegmatites enriched in high-field-strength elements. These pegmatites are of NYF (niobium-yttrium-fluorine) geochemical type and served as the principal source of Be, 5(, Nb, Ta, and rare-earth elements (REE) that were liberated and redeposited as rare Be-As-Y-REE minerals, including the As-rich fergusonite-beta-(Y). The latter mineral crystallizes with monoclinic symmetry [a - 5.1794(14), b = 11.089(3), c = 5.1176(14) [Angstrom], [beta] = 91.282(8)[degrees], V= 293.87(14) [[Angstrom].sup.3], space group 12/a] and has the empirical formula [([Y.sub.0.70][Dy.sub.0.07][Er.sub.0.05] [Ca.sub.0.05][Gd.sub.0.02][U.sub.0.02][Yb.sub.0.01] [Tb.sub.0.01][Th.sub.0.01][Nd.sub.0.01])[SIGMA]0.95] [([Nb.sub.o.68][As.sup.5+.sub.0.27][W.sub.0.06] [Ta.sub.0.01][Si.sub.0.01]).sub.[SIGMA]1.03][O.sub.4]. The crystal structure of fergusonite-beta-(Y) has been refined using a thermally untreated single crystal to [R.sub.1] = 6.6% for 441 observed reflections with [F.sub.o]/[sigma][F.sub.o] > 4. The incorporation of As in the structure of monoclinic fergusonite-type phases is discussed in the context of the data available for synthetic analogs. Keywords: Fergusonite, single crystal, X-ray diffraction, EMPA DOI: 10.2138/am.2010.3239

In this study, the mineral chemistry and alteration of bastnasite-(Ce), parisite-(Ce), and synchysite-(Ce) was investigated by EMPA, TG, DTG, CHNS, and SCXRD techniques. Relevant chemical data on light and volatile elements and X-ray diffraction data useful to evaluate the effect of OH content on the unit-cell volume &such carbonates are provided. Significant amounts of OH in both the parisite-(Ce) and synchysite-(Ce) were found, and these data are the first direct evidence of hydration for these carbonates. Single-crystal X-ray diffraction data showed that hydration causes an increase in the unit-cell volume for parisite and synchysite. Parisite-(Ce) and synchysite-(Ce) OH end-members have not been described in nature so far, and the amount of water must be taken into account for evaluating changes in stability field conditions. Textural relationships and replacement processes are discussed. Keywords: Ca-REE carbonates, Mount Malosa, Malawi, hydration

Aluminocerite-(Ce), ideally [(Ce,Ca).sub.9]Al[(Si[O.sub.4]).sub.3] [[Si[O.sub.3](OH)].sub.4][(OH).sub.3], is isostructural with cerite-(Ce) and cerite-(La). The holotype was found at the Ratti quarry, near Baveno, Italy, in millimeter-sized secondary cavities hosted in aplite-pegmatite veins and pods within pink granite. Aluminocerite-(Ce) forms aggregates of pseudo-octahedral to rhombohedral crystals flattened on the c axis. The cotype of aluminocerite-(Ce) was discovered at the Locatelly quarry, also near Baveno, where it occurs in centimeter-sized miarolitic cavities in pink granite. The mineral is pale pink to pink-reddish, with a white streak, and is translucent with a vitreous luster. Aluminocerite-(Ce) is non-fluorescent. The hardness based on the Mohs scale is 5, and the tenacity is brittle. Neither cleavage, fracture, or twinning were observed. Calculated density is 4.675 g/[cm.sup.3]. It is uniaxial, optically positive, with [n.sub.o] = 1.810-1.816 and [n.sub.e] = 1.812-1.822 ([lambda], = 589 nm) and non-pleochroic. The average of 15 electron microprobe analyses for the holotype gave (wt%): [Ce.sub.2][O.sub.3] 23.37; [Nd.sub.2][O.sub.3] 15.59; [La.sub.2][O.sub.3] 7.43; [Sm.sub.2][O.sub.3] 4.38; [Pr.sub.2][O.sub.3] 3.54; [Gd.sub.2][O.sub.3] 3.12; [Y.sub.2][O.sub.3] 1.68; [Dy.sub.2][O.sub.3] 0.46; [Yb.sub.2][O.sub.3] 0.07; CaO 8.31; [Fe.sub.2][O.sub.3] 0.47; [Al.sub.2][O.sub.3] 2.47; Si[O.sub.2] 24.01; and [H.sub.2]O 3.63 (calculated from crystal-chemical constraints), total 98.53 wt%, corresponding to the empirical formula [([Ca.sub.2.60][Ce.sub.2.49][Nd.sub.1.62][La.sub.0.80][Sm.sub.0.44] [Pr.sub.0.38][Gd.sub.0.30][Y.sub.0.26][Dy.sub.0.04][Yb.sub.0.01]).sub.[SIGMA] 8.94][([Al.sup.3+.sub.0.85][Fe.sup.3+.sub.0.10]).sub.[SIGMA]0.95] [(Si[O.sub.4]).sub.3][[Si[O.sub.3](OH)].sub.4] [(OH).sub.3.06], calculated on the basis of Si = 7. Aluminocerite-(Ce) is trigonal, space group R3c, with a =10.645(1), c = 38.019(5) [Angstrom], V = 3731 [[Angstrom].sup.3]. The strongest eight lines in the X-ray powder diffraction pattern are [d in [Angstrom] (I)(hkl)]: 3.405(27)(122), 3.250(26)(124), 2.914(100)(02,10), 2.647(58)(220), 2.198(40)(03,12), 1.923 (34) (238), 1.826(24)(051), and 1.732(46)(03,18). The crystal structure has been refined to R1 = 0.056 for 745 observed reflections. The name is an allusion to the fact that it is the Al-dominant analog of cerite-(Ce). Keywords: Aluminocerite-(Ce), single-crystal XRD, EMP analyses, new mineral, Raman spectroscopy

The new mineral marchettiite (IMA2017-066) is the natural equivalent of ammonium hydrogen urate. It has a simple molecular formula C5H7N5O3 and can be alternatively written as (NH4)C5H3N4O3. Marchettiite was found in a cleft at Mount Cervandone, Devero Valley, Piedmont, Italy, where it occurs as aggregates of opaque pale pink to white, platy prismatic crystals. This mineral has a white streak, dull and opaque lustre, it is not fluorescent and has a hardness of 2–2.5 (Mohs' scale). The tenacity is brittle and crystals have a good cleavage parallel to {001}. The calculated density is 1.69 g/cm3. Marchettiite is biaxial (–) with 2V of 47.24°; the optical properties of marchettiite were determined by periodic-DFT methods providing the following values: α = 1.372, β = 1.681 and γ = 1.768. No twinning was observed. Electron microprobe analyses gave the following chemical formula: C4.99H6.97N4.91O3.00. Although the small crystal size did not allow refinement of structural data by single-crystal diffraction, we were able to refine the structure by powder micro X-ray diffraction. Marchettiite has space group P $\bar{1}$ and the following unit-cell parameters: a = 3.6533(2) Å, b = 10.2046(7) Å, c = 10.5837(7) Å, α = 113.809(5)°, β = 91.313(8)°, γ = 92.44(1)° and V = 360.312 Å3. The strongest lines in the powder diffraction pattern [ d in Å (I)(hkl)] are: 9.784(50)(001); 8.663(80)(01 $\bar{1}$); 5.659(100)(011); 3.443(100)(10 $\bar{1}$); 3.241(70)(003) and 3.158(100)(1 $\bar{1}\bar{1})$. Marchettiite is named after Gianfranco Marchetti, the mineral collector who found this mineral. [ABSTRACT FROM AUTHOR]

The high-pressure behavior of the natural arsenate gasparite-(Ce) [Ce0.43La0.24Nd0.15Ca0.11Pr0.04Sm0.02Gd0.01(As0.99Si0.03O4)] from the Mt. Cervandone mineral deposit (Piedmont Lepontine Alps, Italy), has been studied by in situ single-crystal synchrotron X-ray diffraction up to 22.01 GPa. Two distinct high-pressure ramps have been performed, using a 16:3:1 methanol:ethanol:water solution and helium as P-transmitting fluids, respectively. No phase transition occurs within the pressure range investigated, whereas a change in the compressional behavior has been observed at ~ 15 GPa. A second-order Birch-Murnaghan EoS was fitted to the P-V data, leading to a refined bulk modulus of 109.4(3) GPa. The structural analysis has been carried out on the basis of the refined structure models, allowing the description of the deformation mechanisms accommodating the bulk compression in gasparite-(Ce) at the atomic scale, which is mainly controlled by the compression of the Rare Earth Elements coordination polyhedra, while the AsO4 tetrahedra behave as a quasi-rigid units. A micro-Raman spectroscopy analysis, performed at ambient conditions, suggests the presence of hydroxyl groups into the structure of the investigated gasparite-(Ce). [ABSTRACT FROM AUTHOR]

Poldervaartite was described in 1993, based on attractive specimens collected at the Wessels mine in South Africa. Around 2001 a bonanza of fine specimens presumed also to be poldervaartite was [...]

The crystal structure and crystal chemistry of meyerhofferite, ideally CaB3O3(OH)5·H2O, was investigated by a multi-methodological approach based on titrimetric determination of boron, gravimetric determination of calcium, determination of fluorine by ion selective electrode, determination of water content by heating, other minor elements by inductively coupled plasma atomic emission spectroscopy, along with single-crystal synchrotron X-ray and neutron diffraction. The concentration of more than 50 chemical elements was measured. The combination of these techniques proves that the composition of meyerhofferite approaches the ideal one (i.e., (Ca1.012Mg0.003) (B2.984Si0.001)O3(OH)5·1.018H2O), with only a modest fraction of Mg (with MgO ≈ 0.03 wt%) replacing Ca, and with Si the only potential substituent of tetrahedral B (with SiO2 ≈ 0.02 wt%). The content of REE and other minor elements is, overall, not significant, including that of fluorine as a potential OH− substituent (i.e., < 0.01 wt%). These findings have some relevant geochemical and technical implications, here discussed. The X-ray and neutron structure model obtained in this study prove that the building units of the structure of meyerhofferite consist of: two BO2(OH)2 tetrahedra and one BO2(OH) triangle, linked by corner-sharing to form [B3O3(OH)5]2− rings, and distorted Ca-polyhedra (with CN = 8, CaO3(OH)4(OH2)), linked by edge-sharing to form infinite chains along [001]. The B3O3(OH)5 rings are connected to the Ca-polyhedra chains by corner- and edge-sharing, on two sides of the chains. These heteropolyhedral chains, made by Ca-polyhedra and B3O3(OH)5 rings, are mutually connected through hydrogen bonding only, giving rise to the tri-dimensional edifice of meyerhofferite. The neutron structure refinement showed no evidence of static or dynamic disorder pertaining to the H sites; their libration regime was found to be significantly anisotropic. At least seven of the nine oxygen sites of the structure are involved in H-bonding, as donors or as acceptors. The role played by the H-bonding scheme on the physical properties of meyerhofferite is discussed. [ABSTRACT FROM AUTHOR]

The Perticara mine area in northern Italy has long been famous among mineralogists as a source of superb crystallized sulfur. Mined since Roman times, it has yielded the world's largest [...]

Kernite, ideally Na2B4O6(OH)2∙3H2O, is a major constituent of borate deposits and one of the most important mineral commodities of B. The chemical composition and crystal structure of kernite from the Kramer Deposit (Kern County, California) were investigated by a suite of analytical techniques (i.e., titrimetric determination of B content, gravimetric method for Na, ion selective electrode for F, high-T mass loss for H2O content, inductively coupled plasma atomic emission spectroscopy for REE and other minor elements, elemental analysis for C, N, and H contents) and single-crystal X‑ray (at 293 K) and neutron (at 20 K) diffraction. The concentrations of more than 50 elements were measured. The general experimental formula of the kernite sample used in this study is Na1.99B3.99O6(OH)2∙3.01H2O. The fraction of other elements is, overall, insignificant: excluding B, kernite from the Kramer Deposit does not act as geochemical trap of other technologically relevant elements (e.g., Li, Be, or REE). The X‑ray and neutron structure model obtained in this study confirms that the structure of kernite is built up by: two (crystallographically independent) triangular BO2OH groups and two tetrahedral BO4 groups, which share corner-bridging O atoms to form threefold rings, giving chains running along [010], and NaO4(OH)(OH2) and NaO2(OH)(OH2)3 polyhedra. Positional disorder of two H sites of H2O molecules was observed by the neutron structure refinement and corroborated by the maximum-entropy method calculation, which consistently provided a model based on a static disorder, rather than a dynamic one. The H-bonding network in the structure of kernite is complex, pervasive, and plays a primary role on its structural stability: the majority of the oxygen sites are involved in H-bonding, as donors or as acceptors. The potential utilizations of kernite, as a source of B (B2O3 ~50 wt%), are discussed, on the basis of the experimental findings of this study. [ABSTRACT FROM AUTHOR]

The Tanno pegmatitic field, placed southward of Chiavenna (Central Alps, Sondrio, Italy), develops a large number of subplanar dykes that crosscut the Chiavenna Unit, an ophiolitic complex mainly composed, in the study area, of amphibolite rocks. This study focuses on the contact between a pegmatitic dyke and the amphibolitic country rock. We distinguished four zones across the contact: I) inner amphibolite, II) contact amphibolite, III) contact pegmatite, IV) inner pegmatite. The inner amphibolite, not affected by melt-rock interaction, is composed of amphibole, phlogopite, ilmenite, titanite and rutile. Two amphibole generations occur, both of them showing a patchy compositional zoning. Amphibole I are Mg-hornblende, whereas Amphibole II have a pargasitic composition. The contact amphibolite shows an enrichment of mica belonging to the phlogopite-biotite series, titanite and the presence of fluorapatite and plagioclase (Ab45-60), that is absent in the inner amphibolite. Close to the contact, amphiboles display no zoning and gain an Mg-horneblenditic composition. The contact pegmatite has quartz, albitic plagioclase, garnet (almandine-spessartine series), muscovite, K-feldspar and fluorapatite. It shows a comb texture, with elongation of plagioclase crystals normal to the contact itself. Far from the contact, the inner pegmatite has an increasing grain-size and a less organized texture. In this zone several accessory phases occur, including gahnite, columbite-(Fe), monazite-(Ce), xenotime-(Y), uraninite and betafite. Whole rock analyses suggest that a chemical exchange, concerning both major elements and trace elements, occurred between the pegmatitic melt and the hosting amphibolite. A considerable increase of SiO2, Na2O and, to a lesser extent, of Al2O3 is observed from the amphibolite towards the pegmatite; K2O and CaO show a decrease at the same extent. The REE pattern in the pegmatite highlights an enrichment in HREE at the contact. Mineral chemistry confirms this trend with variations observable in plagioclase, gradually more albitic from the amphibolite to the pegmatite. Mineralogical characters and geochemical features allow to classify the Tanno pegmatite in the LCT (Lithium, Cesium, Tantalium) family. Based on the metamorphic peak conditions reported from the Lepontine Dome the ambient conditions during pegmatite intrusion were ca. 550°C and 5 kbar. The reduced thermal difference between pegmatite and wall rock explains the diffuse contact observed by X-ray micro-computed tomography. The collected data suggest a chemical interaction between melt and wall rock, according to the following reaction taking place in the amphibolite [ABSTRACT FROM AUTHOR]

The crystal structure and crystal chemistry of wardite, ideally NaAl3(PO4)2(OH)4·2H2O, was investigated by single-crystal neutron diffraction (data collected at 20 K) and electron microprobe analysis in wavelength-dispersive mode. The empirical formula of the sample used in this study is: (Na0.91Ca0.01)Σ = 0.92(Al2.97Fe3+0.05Ti0.01)Σ = 3.03(P2.10O8)(OH)4·1.74H2O. The neutron diffraction data confirm that the crystal structure of wardite can be described with a tetragonal symmetry (space group P41212, a = b = 7.0577(5) and c = 19.0559(5) Å at 20 K) and consists of sheets made of edge-sharing Na-polyhedra and Al-octahedra along with vertex-sharing Al-octahedra, parallel to (001), connected by P-tetrahedra and H bonds to form a (001) layer-type structure, which well explains the pronounced {001} cleavage of the wardite crystals. The present data show that four crystallographically independent H sites occur in the structure of wardite, two belonging to a H2O molecule (i.e., H1–O6–H2) and two forming hydroxyl groups (i.e., O5–H3 and O7–H4). The location of the hydrogen atoms allows us to define the extensive network of H bonds: the H atoms belonging to the H2O molecule form strong H bonds, whereas both the H atoms belonging to the two independent hydroxyl groups form weak interactions with bifurcated bonding schemes. As shown by the root-mean-square components of the displacement ellipsoids, oxygen and hydrogen atoms have slightly larger anisotropic displacement parameters compared to the other sites (populated by P, Al and Na). The maximum ratio of the max and min root-mean-square components of the displacement ellipsoids is observed for the protons of the hydroxyl groups, which experience bifurcated H-bonding schemes. A comparative analysis of the crystal structure of wardite and fluorowardite is also provided. [ABSTRACT FROM AUTHOR]