1,721,130 research outputs found
Determinazione quantitativa del contenuto in OH delle vesuvianiti attraverso microspettroscopia FT-IR
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The channel constituents of cancrinite-group minerals. Micro- and Mesoporous Mineral Phases
No full textThe temperature behaviour of water in leucite
No full textNaturally leucite crystallizes in the cubic phase, with space group Ia3d (Peacor, 1968). On cooling below T = 625°C it undergoes a phase transition to a tetragonal I4/a form (Mazzi et al. 1976); there are indications, however, that an additional tetragonal phase is stable over a narrow temperature interval (Lange et al. 1986). Palmer et al. (1997) have shown that the displacive phase transition to tetragonal symmetry is due to twisting of tetragonal prisms of corner-linked (Al,Si)O4 tetrahedra about [001] and a collapse of the [111] structural channels with concomitant volume reduction. Although nominally anhydrous (NAM), leucite typically contains significant amounts of water; this feature was reported for samples from Roccamonfina (Balassone et al., 2006) and the Alban Hills volcano (Della Ventura et al., 2008). Della Ventura et al. (2008) have shown in addition that H2O may be significantly zoned, thus providing a potential tool to monitor the evolution of the magmatic conditions with time. More recently, Martucci et al. (2011) studied the dehydration of synthetic B-substituted leucite (KBSi2O6) by synchrotron powder diffraction and concluded that the structural modifications accompanying the tetragonal cubic transition is associated with the migration of H2O molecules through the [111] channels.
We relate here a single-crystal high-T in situ FTIR study of a set of natural inclusion-free leucite phenocrystals occurring within lava flows, pyroclastic rocks or ejecta in the Roman Comagmatic Province. The spectra show broad absorptions in the 4000-3000 cm-1 region consisting of overlapping components around 3604, 3500 and 3250 cm-1. Interestingly, two different types of spectra are observed in the H2O stretching region, indicating that water molecules may be trapped in leucite in two different environments (hereafter “type I” and “type II”). These different H2O types are systematically associated with samples from different volcanic areas, thus suggesting a possible role of the petrological conditions (pressure, temperature) of crystallization on the H2O entrapment in leucite. FTIR-FPA images show significant H2O zoning across the samples; crystals with homogeneously-distributed water were selected for the dehydration experiments, done using a Linkam T600 heating stage fitted under a NicPlan FTIR microscope at University Roma Tre. The evolution of the water loss as a function of T was monitored by measuring the principal H2O water absorption. The data indicate a continuous water loss with a break in the trend; in “type I” leucite the slope change occurs at ~ 500°C, and dehydration is complete at T > 600°C, probably close to the transition temperature. In “type II” leucite, the slope change occurs at ~ 350-400°C, and dehydration is complete at ~ 500°C. This behaviour is compared with isostructural materials like analcime or pollucite.
Mazzi, F., Galli, E., and Gottardi, G. (1976) Am. Mineral., 61, 108-115.
Peacor, D.R (1968) Z. Kristall., 127, 213-224.
D.C. Palmer, M.T. Dove, R.M. Ibberson, B.M. Powell (1997) Am. Mineral. 82, 16-29.
G. Balassone, A. Beran, G. Fameli, C. Amalfitano, C. Petti (2006) N. Jahr. Miner. Abh., 182, 149-156
G. Della Ventura, F. Bellatreccia, M. Piccinini (2008) Am. Mineral., 93 1538-1544.
Lange, R.A., Carmichael, LS.E., and Stebbins, IF. (1986) Am. Mineral., 71, 937-945
Channel CO2 in feldspathoids: a review of existing data and new perspectives
No full textThe study of volatile constituents in minerals has potential applications ranging from environmental studies to ore research to volcanic hazards. In this paperwe present new data on the volatile (particularly CO(2)) content of a series of feldspathoids belonging to the cancrinite-sodalite group of minerals, in combination with other data collected over the last few years. The work has been essentially done using FTIR microspectroscopy to detect and characterize the speciation of H and C in the micropores of these minerals. We show that most cancrinite-sodalite group of minerals are able to trap CO(2) in their structure in addition to other molecular and anionic species such as H(2)O, OH, F, Cl, SO(4), SO(3) etc. A combination of in situ and annealing heat-treatments shows that the different species in the cancrinite-sodalite group release CO(2) at different temperatures, due to the different connectivity of their pores. Detailed FTIR microspectrometry mappings typically show non-homogeneous distributions of hydrogen and carbon across the samples, and suggest a possible use of these minerals as a tool for geothermometric modelling. The finding that most cancrinite-sodalite group minerals are able to trap carbon dioxide opens a new frontier in the design of materials having potential for carbon sequestration from the atmosphere
Channel CO<sub>2</sub> in feldspathoids: new data and new perspectives
No full textThe study of volatile constituents in minerals has potential applications
ranging from environmental studies to ore research to volcanic hazards.
In this paperwe present newdata on the volatile (particularlyCO2) content of a
series of feldspathoids belonging to the cancrinite-sodalite group of minerals,
in combination with other data collected over the last few years. The work has
been essentially done using FTIR microspectroscopy to detect and characterize
the speciation of H and C in the micropores of these minerals. We show
that most cancrinite-sodalite group of minerals are able to trap CO2 in their
structure in addition to other molecular and anionic species such as H2O, OH,
F, Cl, SO4, SO3 etc. A combination of in situ and annealing heat-treatments
shows that the different species in the cancrinite-sodalite group release CO2 at
different temperatures, due to the different connectivity of their pores.Detailed
FTIR microspectrometry mappings typically show non-homogeneous distributions
of hydrogen and carbon across the samples, and suggest a possible
use of these minerals as a tool for geothermometric modelling. The finding
that most cancrinite-sodalite group minerals are able to trap carbon dioxide
opens a new frontier in the design of materials having potential for carbon
sequestration from the atmosphere
New crystal-chemical and structural data of dietrichite, ideally ZnAl<sub>2</sub>(SO<sub>4</sub>)<sub>4</sub>•22H<sub>2</sub>O, a member of the halotrichite group
No full textNew crystal-chemical and structural data of a sample of dietrichite, ideally ZnAl2(SO4)4·22H2O, from the pyrite mine of
Boccheggiano, Grosseto, Italy, are reported. This sample, unlike holotype dietrichite, is very close to the ideal chemical composition, in fact combined ICP and thermogravimetry indicate a formula (Zn0.98Fe0.07)Al1.91(SO4)4.03·21.88H2O based on 38O. The crystal structure has been refined by the Rietveld method on transmission X-ray powder diffraction data (Rp = 4.13%, Rwp = 5.44%, RB = 4.66%). Dietrichite is monoclinic P21/c, Z = 4, a = 6.1757(2), b = 24.262(1), c = 21.206(1) Å, = 100.436(3)°. The structure of
dietrichite consists of one ZnO(H2O)5 octahedron, two independent Al(H2O)6 octahedra, and four independent SO4 tetrahedra per
asymmetric unit. The only direct connection between polyhedra is by sharing of an oxygen atom, O(16), between S(4) and Zn. The
structure contains 22 water molecules, 17 of which are octahedrally co-ordinated with Zn and Al cations whereas the remaining five
molecules are only linked via hydrogen bonds to O or other H2O molecules. Hexagonal channels, running along [100], originate from
a regular alternation of one ZnO(H2O)5 octahedron, two Al(H2O)6 octahedra, and three SO4 tetrahedra. Within the structure two types
of channels may be identified, the first one containing three and the second two H2O molecules. Band positions of the IR spectrum
of dietrichite are consistent with those of reference data
Datolite: a new occurrence in volcanic ejecta (Pitigliano, Tuscany, Italy) and crystal-structure refinement
No full textThis paper describes the first occurrence of datolite in a volcanic ejectum collected at Pitigliano, Vulsini volcanic complex, Toscana, Italy. The studied specimen was sampled within the pyroclastic levels erupted during one of the several eruptive phases of the Latera caldera in the Roman Comagmatic region (253 - 166 ka). The host rock is massive, with a syenitic appearance, and consists of predominant sanidine, both as fine-grained groundmass and phenocrystals up to 1 cm long. Associated minerals are andraditic garnet, clinopyroxene (augite), biotite, iron oxide and vishnevite. Datolite occurs within vugs in the ejectum as well-formed, transparent, colourless crystals, with stubby prismatic shape; the crystals are about 0.5 mm in maximum diameter. The crystal structure of datolite from Pitigliano has been refined in the P21/c space group to R = 2.18%. Cell dimensions are: a (Å) = 4.8318(4), b (Å) = 7.6116(3), c (Å) = 9.6380(2), b (°) = 90.141(4), V (Å3) = 354.46(3). The chemical composition is (Ca2.006K0.001)Σ2.007(Fe0.007Mn0.004Mg0.002)Σ0.013(B1.986Si1.988Al0.026)Σ4.000O8(OH1.962O0.026F0.012)Σ2.000 and the density calculated on the basis of composition and cell dimensions is Dc = 3.00 g/cm3
Single-crystal FTIR spectroscopy of masutomilite, the Mn-analogue of zinnwaldite
No full textMasutomilite is a rare Mn-analogue of zinnwaldite, which was firstly described from a granitic pegmatite at Tanakamiyama, Shiga Prefecture, Japan. Masutomilite forms extensive solid-solutions with zinnwaldite; few samples on this system have been actually reported from Tawara, Gifu Prefecture, Japan from western Moravia, Czech Republic and from few other localities. We relate here an infrared study of three mica samples labeled as masutomilite from Japan (Hirukawa Mine, Gifu Prefecture), Central Urals, Russia (Mokrusha Pegmatite, Murzinka Region) and Idaho, USA (Santooth Mountains, Boise County). Microchemical data, although incomplete due the lack of H2O determination, showed that the studied micas from Japan and USA have different Fe/Mn contents, the Idaho sample being significantly enriched in Fe relative to Mn. The Russian sample did not show any Mn and a only a very small amount of Fe (< 1 wt%). Single-crystal, polarized-light FTIR spectra were collected for all samples using a NicPlan microscope equipped with a nitrogen-cooled MCT detector, a KBr beamsplitter and a gold wire grid polarizer, at 4 cm-1 resolution, with a spot size ~ 100 μm. Single cleavage flakes, 10 to 20 μm thick, were oriented under the optical microscope on the basis of the interference figure (masutomilite is biaxial negative, with Y = b and 2V < 35°), and polarized spectra were collected with the electric vector E//γ and E//β. The flakes were then mounted on a glass capillary and stepwise tilted under the beam, in order to collect the α-polarization spectra. The collected patterns are significantly different, due to the different chemical composition of the examined samples, however they show broad similarities. In particular they consist of a higher-frequency (~ 3700 cm-1) component, which is assigned to OH groups in local tri-octahedral environments, and broader absorptions at frequencies < 3600 cm-1, assigned to OH-groups in local di-octahedral environments. This feature indicates that all analyzed samples have vacant octahedral sites in the vicinity of the OH-group. In both samples from Utah and Japan, the most intense band at around 3600 cm-1 consists of several (at least four) well-resolved components, while the same absorption in the Russian specimen consists of a single band. This difference is explained considering the presence of Mn and Fe in the former samples, and of a unique octahedral cation (Al) in the latter sample. The higher-frequency, 3700 cm-1 band, is strongly polarized for all specimens, with maximum absorption for E//α, indicating that the trioctahedral OH groups are aligned along the c crystallographic axis. The di-octahedral bands are also significantly polarized and show maximum absorption for E//γ. From measurement of the dichroic ratio (absorbance along a / absorbance along b) the orientation of the di-octahedral O-H vector in the (001) place can also be evaluated
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