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Single-crystal, polarized-light, FTIR spectroscopy of masutomilite: short range order of cations and orientation of the O-H dipoles
No full textMasutomilite is a rare Mn-analogue of the Li-mica zinnwaldite; it was described by Harada et al. (1976) from the Shiga Prefecture, Japan, and later reported from few other localities (Němec, 1983, Čerńy and Burt, 1984). We relate here an infrared study of two masutomilite specimens from Central Urals, Russia (Mokrusha Pegmatite, Murzinka Region) and Idaho, USA (Sawtooth Mountains, Boise County), respectively. Both samples belong to the 1M polytype. The chemical composition, derived by combining electron microprobe analysis, inductively coupled plasma atomic emission spectrometry (ICP-AES) for Li, and results from the structure refinement are, on the basis of O10(F,OH)2 (Brigatti et al., 2007): (Si3.30Al0.70) (Al1.00Fe0.36Mg0.01Mn0.31Li1.32) (Ca0.01Na0.04K0.94) O10F1.91(OH)0.09 (Mokrusha mine, Russia) and (Si3.11Al0.89) (Al0.91Ti0.02Fe0.46Mg0.03Mn0.52Li1.06) (Na0.05K0.92Rb0.02) O10F1.89(OH)0.11 (Sawtooth Mountains, Boise County, Idaho, USA). Both samples have all Li > 1.0 apfu and variable Fe/Mn. The anionic site is dominated by F with low amounts of OH (0.09-0.12 apfu). Single-crystal, polarized-light FTIR spectra were collected 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. The spot size was ~ 100 μm and 128 scans were averaged for each spectrum. The collected patterns are different as expected from the different chemical composition of the examined samples, however they show broad similarities and a similar behaviour under polarized light. They consist of a higher-frequency component which is centred at 3685 and 3659 cm-1 for masutomilite from Russia and Idaho, respectively; both bands are strongly polarised for E // α. A broader, multicomponent absorption is observed at around 3600 cm-1. In masutomilite from Idaho this band is split in two components of equal intensity, at 3685 and 3659 cm-1 respectively, plus a lower-frequency shoulder at ~ 3552 cm-1. This band shows maximum intensity for E // γ and a medium intensity for E // α, while showing reduced intensity for E // β. A lower frequency, broad band is finally present at ~3500 cm-1 in both samples; this feature is virtually unaffected by rotation of the polarizer. Following the model of Robert et al. (1989) for Li-bearing micas, the higher frequency bands at 3685 - 3659 cm-1 are assigned to OH-dipoles bonded to FeFeFe local environments (TRI-6 environments), while the multicomponent band around 3600 cm-1 is assigned to AlM2+M2+ (with M2+ = Fe or Mn) local environments (TRI-7 environments). The spectra show that all Li is associated to F at the anionic site. From measurement of the dichroic ratio (absorbance along a / absorbance along b, e.g. Serratosa and Bradley, 1962, Vedder and McDonald, 1963) the orientation of the O-H vectors with respect the (001) plane can be evaluated.
References
Brigatti, M.F., Mottana, A., Malferrari, D. and Cibin, G. (2007) Am. Mineral., 92, 1395-1400.
Harada, K., Honda, M., Nagashima, K., Kanisawa, S. (1976) Min. J., 8, 95-109.
Němec, J. (1983) Neues J. Miner., Mh., 537-540.
Robert, J.-J., Beny, J.-M., Beny, C., Volfinger, M. (1989) Can. Mineral., 27, 225-235.
Serratosa, J.M. and Bradley, W.F. (1962) Determination of the orientation of OH bond axis in layer silicates by infrared absorption. J. Phys. Chem., 62, 1164-1167.
Vedder, W. and McDonald, R.S. (1963) Vibrations of the OH ions in muscovite. J. Chem. Phys., 38, 1583-1590
Iron environment in a Montmorillonite from Gola del Furlo (Marche, Italy). A Synchrotron Radiation XANES and a Moessbauer study.
No full textMineralogia di Roma e della sua campagna. The Minerals of Rome and of the surrounding areas
No full textSono raccolti tutti i dati storici e scientifici più aggiornati sulle 15 specie mineralogiche di cui Roma e la zona circostante
compresa tra i laghi di Bracciano (a Nord) e di Nemi (a Sud) sono la località-tipo, integrandoli con la documentazione fotografica
delle loro forme morfologiche caratteristiche. Inoltre, è compilata la lista completa di tutti i minerali, sia isolati ed appariscenti
sia in aggregati e formativi di rocce, che sono presenti nella stessa area, distinguendoli tra sedimentari e vulcanici e richiamandone
il significato petrogenetico, vale a dire il loro contributo a definire le condizioni di pressione e temperatura alle quali si è evoluta
la geologia dell’area romana in età quaternaria. In particolare, sono messe in evidenza le particolarità mineralogiche dovute alle
attività vulcaniche e geotermiche nei Colli Albani e nei Monti Sabatini, i due complessi su cui è fondata la città di Roma.All updated data of scientific and historical interest on the 15 mineral species first described in Rome and in the surrounding area i.e., from lake
Bracciano, to the North, to lake Nemi, to the South, are assembled and discussed. Their typical morphologies are also presented as photographs. In addition, a full
list of all minerals described over the area is given. A distinction is made between minerals occurring as euhedral, conspicuous crystals and those present as rock
forming grains. Most minerals are discussed with reference to their significance for establishing the pressure and temperature conditions at which they formed, with
special attention for those occurring in the lavas and pyroclastics related either to the Sabatini volcanic complex or to the Alban Hills volcano, both belonging to the
world-renowned Roman Comagmatic Region. The few sedimentary minerals of palaeomagnetic and geothermal significance in the Tiber valley and in ancient lakes
and ponds scattered through the Roman campaign are also listed and briefly discussed
New Rare Earth Minerals in the Sanidinitic ejecta within Pyroclastic rocks of the Roman Potassic Province
No full textSingle-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
Thaumasite from the Tschwinning Mine, South Africa
No full textThaumasite from the manganese mine of Tschwinning, South Africa, has the formula Ca3.097 Si1.062OH6.372(CO3)0.994(SO4)1.000·11.596 H2O. Unit cell parameters (a=11.013(2) Å,c=10.379(5) Å,V=1090.1(6) Å3) and refraction indices (ne=1.458(2),n o=1.498(2)) compare well with the best ones available in the literature. The IR spectrum and DT-TG profiles are given. Contradictions between the IR spectrum, a recent structural refinement and the DT-TG are discussed, but cannot be explained satisfactorily
Mineralogia di Roma e della sua campagna
No full textABSTRACT - All updated data of scientific and historical interest on the 15 mineral species first described in Rome and in the surrounding area i.e., from lake
Bracciano, to the North, to lake Nemi, to the South, are assembled and discussed. Their typical morphologies are also presented as photographs. In addition, a full
list of all minerals described over the area is given. A distinction is made between minerals occurring as euhedral, conspicuous crystals and those present as rock
forming grains. Most minerals are discussed with reference to their significance for establishing the pressure and temperature conditions at which they formed, with
special attention for those occurring in the lavas and pyroclastics related either to the Sabatini volcanic complex or to the Alban Hills volcano, both belonging to the
world-renowned Roman Comagmatic Region. The few sedimentary minerals of palaeomagnetic and geothermal significance in the Tiber valley and in ancient lakes
and ponds scattered through the Roman campaign are also listed and briefly discussed
Asbestiform tremolite within the late pyroclastic deposits of the Alban Hills volcano (Latium, Italy): FTIR spectroscopy and crystal chemistry
No full textThis work relates the occurrence and the characterization of fibrous tremolite within the latest pyroclastic deposits of the Colli Albani (Alban Hills) volcano, to the south-east of Rome (Italy). These mineralizations were observed during a systematic rock sampling undertaken to complete the geological survey for the new 1:50,000 map of this volcanic area. The examined specimens were collected inside distal deposits correlated to the last Albano Maar activity, which are geographically located within the boundaries of the Nemi community. Tremolite occurs within both carbonate ejecta and the host pyroclastic rocks. It shows up as whitish to light grey-coloured aggregates of crystals with fibrous aspect and sericeous brightness. Due to the extremely small crystal dimensions, never exceeding 0.5 mu m in diameter, the micro-chemical composition of the fibres could be obtained only by combining P-XRD, SEM-EDX and FTIR methods. Infrared spectroscopy, in particular, proved to be a valuable technique to characterize the studied amphibole. The composition determined is that of a Fe-free F-rich (c. 53 %) tremolite with significant (c. 20 %) richterite components in solid solution. The occurrence of fibrous tremolite in an inhabited place, occurring as natural geological material rather than being due to anthropogenic pollution, should be examined with concern, because it implies complex health and legal responsibilities in the case of mobilization due to extreme climatic events
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