ORCID Profile
0000-0001-8348-7181
Current Organisation
Università degli Studi di Milano
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Publisher: Springer Science and Business Media LLC
Date: 10-2016
Publisher: Mineralogical Society of America
Date: 29-10-2012
DOI: 10.2138/AM.2012.4232
Publisher: Mineralogical Society of America
Date: 07-2008
DOI: 10.2138/AM.2008.2965
Publisher: Mineralogical Society of America
Date: 11-2009
DOI: 10.2138/AM.2009.3237
Publisher: Mineralogical Society of America
Date: 17-09-2010
DOI: 10.2138/AM.2010.3554
Publisher: Mineralogical Society of America
Date: 22-12-2010
DOI: 10.2138/AM.2011.3595
Publisher: Mineralogical Society
Date: 06-2014
DOI: 10.1180/MINMAG.2014.078.3.15
Abstract: A single-crystal neutron diffraction study of oxy-dravite from Osarara (Narok district, Kenya) was performed. Intensity data were collected in Laue geometry at 10 K and anisotropic-structure refinement was undertaken. For the first time, two independent H sites were refined unambiguously for a mineral belonging to the tourmaline supergroup and located at 0.26, 0.13, 0.38 (labelled as H3, site occupancy ∼98%) and at 0, 0, 0.9 (labelled as H1, site occupancy ∼25%). The H-bonding scheme can thus be defined as follows: (1) the O at the O3 site acts as a ‘donor’ and the O at the O5 site as ‘acceptor’, the refined O3–H3 bond distance is 0.972(2) Å (and 0.9946 Å corrected for “riding motion”), H3⋯O5 = 2.263(2) Å, O3⋯O5 = 3.179(1) Å and O3–H3⋯O5 = 156.6(1)° (2) the oxygen at the O1 site acts as a ‘donor’ and the O atoms at O4 and O5 as ‘acceptors’, the refined O1–H1 bond distance is 0.958(8) Å (and 0.9833 Å corrected for “riding motion”), H1⋯O4 = 2.858(6) Å, O1⋯O4 = 3.378(1) Å and O1–H1⋯O4 = 115.12(1)°, whereas H1⋯O5 = 2.886(6) Å, O1⋯O5 = 3.444(1) Å and O1–H1⋯O5 = 118.23(1)°. A further test refinement was performed with the H1 site out of the three-fold axis (at 0.02, 0.01, 0.90) this leads to O1–H1 = 0.995(8) Å (and 1.0112 Å corrected for “riding motion”), H1⋯O4 = 2.747(6) Å and O1–H1⋯O4 = 121.7(4)°, whereas H1⋯O5 = 2.654(9) Å and O1–H1⋯O5 = 136.5(6)°. Bond-valence analysis shows that the H-bonding strength involving O3 is stronger than that involving O1: ∼0.11 and .05 valence units, respectively. The refined angle between the O3–H3 vector and [0001] is 3.40(9)°. Such a small angle is in line with a pleochroic scheme for the OH-stretching absorption bands measured by infrared spectroscopy.
Publisher: Mineralogical Society
Date: 06-2014
DOI: 10.1180/MINMAG.2014.078.3.18
Abstract: The crystal structure, H bonding and chemical composition of hydroxylherderite from the Bennett pegmatite, Buckfield, Oxford County, Maine, USA were investigated by single-crystal X-ray diffraction and neutron Laue diffraction, electron microprobe analysis in wavelength-dispersive mode, inductively coupled plasma-atomic emission spectrometry and polarized Raman spectroscopy [ Ca (Na 0.01 Ca 1.01 ) ∑1.02 Be (Be 0.98 Li 0.01 ) ∑0.99 P (Si 0.03 P 0.98 ) ∑1.01 O 4 (OH 0.67 F 0.33 ) ∑1 , Z = 4, a = 9.7856(5), b = 7.6607(5), c = 4.8025(3) Å, β = 90.02(3)°, V = 360.02(4) Å 3 , space group P 2 1 / a ]. The neutron-structure refinement converged with fully anisotropic displacement parameters to give a final agreement index R 1 = 0.0363 for 85 refined parameters and 1614 unique reflections with F o σ( F o ). The structure refinement was used to determine the H position and geometry of H bonding in the structure. One H site was found on the O 5 anion with an O–H interatomic distance, corrected for “riding motion”, of 0.996(2) Å. The H bond of hydroxylherderite is bifurcated with O 2 and O 4 acceptors forming H bonds with O 5⋯ O 2 = 3.163(1) Å, H ⋯ O 2 = 2.544(2) Åand O 5– H ⋯ O 2 = 121.8(1)° O 5⋯ O 4 = 3.081(1) Å, H ⋯ O 4 = 2.428(2) Å and O 5– H ⋯ O 4 = 124.4(1)°. The highly non-linear O–H⋯O hydrogen bonds in hydroxylherderite and in the isotypic datolite [ideally CaBSiO 4 (OH)] are constrained by the tetrahedral network topology. Two main O–H stretching modes were observed in the Raman spectra at 3565 and 3620 cm –1 , which are attributed to the bifurcated H bond. Two additional weak bands at 3575 and 3610 cm –1 are attributed to Si–P disorder in the tetrahedral sites. Results of this study will contribute to the correlation of H-bonding geometry and O–H stretching frequencies of highly non-linear H bonds.
Publisher: Mineralogical Society
Date: 08-2012
DOI: 10.1180/MINMAG.2012.076.4.07
Abstract: We report a single-crystal Fourier-transform infrared (FTIR) study of a s le of pollucite from Maine, USA. Prior to our work, the s le had been characterized by single-crystal X-ray diffraction, neutron diffraction and electron-probe microanalysis. It is cubic Ia 3 d , with a crystal-chemical formula Na 1.93 (Cs 10.48 Rb 0.31 K 0.04 ) Σ=10.83 (Al 14.45 Si 33.97 ) Σ=48.42 O 96 ·3.92H 2 O, and an H 2 O content, determined by thermogravimetric analysis, of 1.6 wt.%. The single-crystal FTIR spectrum has a doublet of intense bands at 3670 and 3589 cm –1 , which are assigned to the ν 3 and ν 1 stretching modes of the H 2 O molecule, respectively. A very intense and sharp peak at 1620 cm –1 is assigned to the ν 2 bending vibration. In the near-infrared region there is a relatively intense peak at 5270 cm –1 , which is assigned to a combination (ν 2 + ν 3 ) mode of H 2 O, and a weak but well defined doublet at 7118 and 6831 cm –1 , which is assigned to the first overtones of the fundamental stretching modes. A relatively weak but extremely sharp peak at 2348 cm –1 shows that the pollucite contains CO 2 molecules in structural cavities. Mapping the s le using FTIR indicates that both H 2 O and CO 2 are homogeneously distributed. Secondary ion mass spectrometry yielded an average CO 2 content of 0.09±0.02 wt.%. On the basis of this value, we determined the integrated molar absorption coefficient for the spectroscopic analysis of CO 2 in pollucite to be εiCO 2 = 11,000±3000 l mol –1 cm –2 the linear molar absorption coefficient for the same integration range is εlCO 2 = 1600±500 l mol –1 cm –1 .
Publisher: Walter de Gruyter GmbH
Date: 07-2012
Publisher: Mineralogical Society of America
Date: 25-06-2012
DOI: 10.2138/AM.2012.4058
Publisher: Schweizerbart
Date: 23-03-2016
Location: Italy
Location: Italy
No related grants have been discovered for G. Diego Gatta.