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- Altieri, Alessandra, et al.
(författare)
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Blue growth zones caused by Fe2+ in tourmaline crystals from the San Piero in Campo gem-bearing pegmatites, Elba Island, Italy
- 2022
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Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 86:6, s. 910-919
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Tidskriftsartikel (refereegranskat)abstract
- Two tourmaline crystals with a blue growth zone at the analogous pole, respectively from the San Silvestro and the Fucili pegmatites, located in the San Piero in Campo village, Elba Island (Tyrrhenian Sea, Italy), have been described for the first time using compositional and spectroscopic data to define their crystal-chemical aspects and the causes of the colour. Compositional data obtained by electron microprobe analysis indicate that both tourmalines belong to the elbaite–fluor-elbaite series. The upper part of each crystal is characterised by an increased amount of Fe (FeO up to ~1 wt.%) and a Ti content below the detection limit. Optical absorption spectra recorded on the blue zone of both samples show absorption bands caused by spin-allowed d-d transitions in [6]-coordinated Fe2+, and no intervalence charge transfer Fe2+-Ti interactions, indicating that Fe2+ is the only chromophore. Mössbauer analysis of the blue zone of the Fucili sample confirmed the Fe2+ oxidation state, implying that the redox conditions in the crystallisation environment were relatively reducing. The presence of colour changes at the analogous termination during tourmaline crystal growth suggests a change in the composition of the crystallisation environment, probably associated with a partial opening of the system.
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| 4. |
- Bernardi, Francesco, et al.
(författare)
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OH-Defects in Detrital Quartz Grains from the Julian Basin (NE Italy and Slovenia): A Fourier Transform Infrared Study
- 2022
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Ingår i: Geosciences. - : MDPI AG. - 2076-3263. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we analyzed up to 80 detrital quartz grains from four lithic greywackes along the stratigraphic column of the Julian Basin, a synorogenic basin in the southeastern Alps between Italy and Slovenia. Fourier transform infrared spectroscopy of detrital quartz was used to investigate the sample set with interest to its OH-defect speciation and content of each associated substitution. According to several recent studies, OH-defects in quartz are correlated to petrogenetic conditions of the source material and can be used as a provenance tool. The aim of this study is to compare results based on this method with previous studies that used other methods, to better constrain the palaeogeographical reconstruction of sedimentary fluxes. Detrital quartz within the samples of the basin shows different patterns of OH-defects and water content, indicating substantial petrogenetic differences between the sediment source rocks. For the oldest analyzed sample (ca. 66 Ma), the distribution of OH-defects suggests a mixed source between igneous and non-igneous rocks, with a predominance of metamorphic material supply. Another sample (56 Ma) reveals a great variability of OH-defects and water content, indicating that the magmatic component dominates over the metamorphic component. The distribution of OH-defects in the samples at the top of the sequence (52–53 Ma) suggests an almost solely metamorphic source. These results are in line with previous studies based on heavy minerals and geochemistry.
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| 5. |
- Cámara, Fernando, 1967-, et al.
(författare)
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Old samples - new amphiboles
- 2022
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Ingår i: Abstracts, International Mineralogical Association 23<sup>rd</sup> General meeting. - Lyon. ; , s. 42-42
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The scientific value of old and well-preserved collections is priceless. Samples that already have been studied and described can still give very useful information. For instance, minerals with complex solid solutions like amphiboles sometimes show new compositions that are feasible because of crystal-chemistry and charge arrangements, based on the current classification scheme by Hawthorne et al. (2012) for the amphibole supergroup. In the last four years, a fruitful collaboration between the Swedish Museum of Natural History and the Department of Earth Sciences of the University of Milan has allowed the identification of new amphibole species, recognized by CNMNC-IMA. First of all, we identified hjalmarite, [ANaB(NaMn)CMg5TSi8O22W(OH)2], which is related to richterite via the homovalent substitution [B]Ca2+ → [B]Mn2+, and is the second recognized member of the sodium–(magnesium–iron–manganese) subgroup, after ferri-ghoseite. Sjögren (1891) had described a physically similar, MnO-rich sample from Långban, named “astochit”. A related amphibole, although belonging to a different subgroup, that we have formally described is potassic-richterite, [AKB(NaCa)CMg5TSi8O22W(OH)2]. It was found in a sample from the Pajsberg iron and manganese ore mines, which was originally collected by the mineralogist Lars Johan Igelström, probably in the 1850s. The most recent amphibole we have described is ferri-taramite [ANaB(NaCa)C(Mg3Fe3+2)T(Si6Al2)O22W(OH)2], found in a skarn sample from the Jakobsberg manganese mine: it was once examined by Flink (1914), who noted the unusual character of the amphibole and described it as a “strange hornblende”.
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- Holtstam, Dan, 1963-, et al.
(författare)
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Ferri-taramite, a new member of the amphibole supergroup, from the Jakobsberg Mn-Fe deposit, Varmland, Sweden
- 2022
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Ingår i: European Journal of Mineralogy. - : Copernicus GmbH. - 0935-1221 .- 1617-4011. ; 34:5, s. 451-462
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Tidskriftsartikel (refereegranskat)abstract
- Ferri-taramite (IMA CNMNC 2021-046), ideally Na-A(B) (CaNa)(C) (Mg3Fe23+)(Si6Al2)O-22(W) (OH)(2), occurs in skarn from the Jakobsberg manganese mine, Varmland, Sweden. Associated minerals are celsian, phlogopite, aegirine-augite, andradite, hancockite, melanotekite, microcline (var. hyalophane), calcite, baryte, prehnite, macedonite and oxyplumboromeite. Conditions of formation, close to peak metamorphism (at circa 650 degrees C and 0.4 GPa), include silica undersaturation, a slightly peralkaline character and relatively high oxygen fugacities. Ferri-taramite forms poikiloblastic crystals up to 5 mm and is dark brownish black with a yellowish grey streak. The amphibole is brittle with an uneven to splintery fracture. Cleavage parallel to {110} is good. Hardness (Mohs) is similar to 6, and D-calc = 3.227(5) g cm(-3). Holotype ferri-taramite has the experimental unit formula (A)(Na0.79K0.16Pb0.01)(Sigma 0.96)(B) (Ca1.26Na0.72Mn0.022+)(Sigma 2)(C )(Mg2.66Mn0.582+ Fe0.162+Zn0.02Fe1.263+ Al0.26Ti0.06)(Sigma)(T)(5.00) (Al1.86Si6.14)Sigma 8O(22)(W) (OH)(2), based on chemical analyses (EDS, laser-ablation ICP-MS) and spectroscopic (Mossbauer, infrared) and single-crystal X-ray diffraction data. The mineral is optically biaxial (-), with alpha = 1.670(5), beta = 1.680(5) and gamma = 1.685(5) in white light and 2 V-meas = 70(10)degrees and 2 V-calc = 70.2 degrees. Ferri-taramite is distinctly pleochroic in transmitted light, with X pale yellow, Y dark brown, Z yellowish brown and absorption Y> Z> X. The eight strongest reflections in the X-ray powder pattern (d values (in angstrom), I-rel, hkl) are 8.44, 60, 110; 3.392, 25, 131; 3.281, 39, 240; 3.140, 100, 310; 2.816, 45, 330; 2.7104, 38, 151; 1.3654, 26, 461; and 1.4451, 33, (6) over bar 61. Refined unit-cell parameters from single-crystal diffraction data are a = 9.89596(13), b = 18.015(2), c = 5.32164(7) angstrom, beta = 105.003(13)degrees and V = 916.38(2) angstrom(3) for Z = 2. Refinement of the crystal structure yielded R = 2.26 % for 2722 reflections with I-0 >2 sigma (I). The Mn2+ and Fe2+ ions show preference for the M1 and M3 octahedrally coordinated sites, whereas Fe3+ is strongly ordered at M2. The A-group cations, K and Na, are split over two subsites, A (m) and A(2), respectively.
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