Hindawi Publishing Corporation International Journal of Mineralogy Volume 2014, Article ID 287069, 6 pages http://dx.doi.org/10.1155/2014/287069 Research Article ‘‘Mohsite’’ of Colomba: Identification as Dessauite-(Y) Erica Bittarello,1 Marco E. Ciriotti,2 Emanuele Costa,1 and Lorenzo Mariano Gallo3 1 DipartimentodiScienzedellaTerra,ViaTommasoValpergaCaluso35,10125Torino,Italy 2 Associazione Micromineralogica Italiana, Via San Pietro 55, 10073 Devesi-Cirie,` Torino, Italy 3 Museo Regionale di Scienze Naturali, Via Giovanni Giolitti 36, 10123 Torino, Italy Correspondence should be addressed to Emanuele Costa; [email protected] Received 11 November 2013; Revised 6 March 2014; Accepted 20 March 2014; Published 8 April 2014 Academic Editor: Elena Belluso Copyright © 2014 Erica Bittarello et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. During a reorganization of the mineralogical collection of Turin University, old samples of the so-called mohsite of Colomba were found. “Mohsite” was discredited in 1979 by Kelly et al., as a result of some analyses performed on the equivalent material coming from the French region of Hautes-Alpes, but the original samples found in similar geological setting in Italy were lost and never analysed with modern equipment. After more than a century, the rediscovered samples of Professor Colomba were analysed by means of SEM-EDS analysis, microRaman spectroscopy, and X-ray diffraction. The results have demonstrated that the historical samples studied by Colomba are Pb-free dessauite-(Y), and pointed to an idealized crystal chemical formula 2+ 3+ 3+ (Sr0.70Na0.25Ca0.09)Σ=1.04(Y0.62U0.18Yb0.09Sc0.08)Σ=0.97 Fe2 (Ti12.66Fe4.78V0.26)Σ=17.70O38 and unit-cell parameters a = 10.376(3) A,˚ c = 3 20.903(6) A,˚ and V = 1949(1) A˚ . 1. Introduction analysis carried out by Colomba showed only the presence of TiO, CaO, FeO, and minor MgO. The data of Colomba were “Mohsite” was first cited in 1827 by Levy´ [1]inrocksamples later summarized by Zambonini [4]. from the Dauphine´ region (France). The identification was These samples (few millimetric size crystals) were lost in obtained mainly on morphological evidence, but the original some drawer of the University Museum Warehouse and for- samples studied by Levy´ were lost, and no other analysis gotten for about a century (Costa and Gallo, [5]). Kelly et al. could be made for a better identification. [6] reported that they had obtained some of the samples of In 1901, Lacroix [2]acquiredsomesamplescomingfrom theLacroixcollectionandgaveadditionaldataonthem. Le Plate Muratouse, La Grave area, at the Department of The analysis performed by Kelly showed the presence Hautes-Alpes (Provence-Alpes-Coteˆ d’Azur, France). Based of Sr and minor Pb, but not calcium, so the mineral of only on the morphological features, very similar to those Lacroix and Colomba was not the new Ca-rich member of described by Levy,´ and considering the close topographical the crichtonite supergroup, which was named loveringite by occurrence, Lacroix identified these samples as “mohsite” Gatehouse et al. [7]. These authors consequently stated that and, since the old types were missing, the new samples the name “mohsite” was incorrectly used for a member of became neotypes. the crichtonite-senaite series, they proposed to discredit the One year later, Colomba [3], at that time, Professor of name “mohsite,” and IMA accepted the proposal. MineralogyattheRoyalUniversityandDirectorofthe In 2008, during the reorganization of the historical Mineralogical Museum of Turin (Piedmont, Italy), described mineralogical collection of the University of Turin, Italy morphologically similar small crystals coming from La (now hosted in the Regional Museum of Natural History Beaume,Oulx(SusaValley,Piedmont,Italy)notsofarfrom of the same town, MRSN hereinafter), some old wooden the French occurrence and in a comparable geological and boxeswereopened,andtheoriginalsamples,togetherwith mineralogical context (Colomba, [3]). Chemical qualitative thehandwrittenlabelofColomba,atthattime,Directorof 2 International Journal of Mineralogy Table 1: Crichtonite supergroup minerals (after Mills et al., 2012 [16]), revised and updated. XII VI IV VI Φ Species A B T2 C18 ( )38 Reference Almeidaite Pb Mn, Y Zn2 Ti, Fe [17] Cleusonite Pb, Sr U (Fe, Zn)2 Ti, Fe [18] Crichtonite Sr, Pb, Ba Mn (Fe, Zn)2 Ti, Fe [19] Davidite-(La) La,Ce,Ca Y,HREE,U (Fe,Mg)2 Ti, Fe, Cr, V [20] Davidite-(Ce) Ce, La Y, HREE, U (Fe, Mg)2 Ti, Fe, Cr, V [20] Dessauite-(Y) Sr, Pb Y, U (Fe, Zn)2 Ti, Fe [8] Gramaccioliite-(Y) Pb, Sr Y, Mn (Fe, Zn)2 Ti, Fe [9] Landauite Na, Pb Mn, Y Zn2 Ti, Fe, Nb [21] Lindsleyite Ba, K Zr, Fe (Mg, Fe)2 Ti, Cr, Fe [22] Loveringite Ca,LREE Zr,Fe (Mg,Fe)2 Ti,Fe,Cr,Al [7] Mapiquiroite Sr, Pb U, Y Fe2 Ti, Fe, Cr [23] Mathiasite K,Ba,Sr Zr,Fe (Mg,Fe)2 Ti, Cr, Fe [22, 24] Paseroite Pb, Sr Mn (Mn, Fe)2 V, Ti , Fe [ 16] Senaite Pb, Sr Mn (Fe, Zn)2 Ti, Fe [19] finding for the Piedmont region and the fourth finding for Italy. 2. The Crichtonite Supergroup The minerals of the crichtonite supergroup belong to Figure 1: Original label manuscript by Colomba. The translation the oxide class containing medium to high size cations from Italian says: “MENACCANITE [sic] (mohsite) crystallized in XII VI albite—Gift of Dr. Colomba—La Beaume (Oulx)” with catalogue (Table 1). The structural formula of the group is A B IV VI XII number (13524). T2 C18(Φ)38,where A=Ba,K,Pb,Sr,La,Ce,Na, VI IV VI Ca; B=Mn,Y,U,Fe,Zr,Sc; T2 =Fe,Mg,Zn; C18 =Ti, Fe,Cr,Nb,V,Mn;and(Φ)38 = O, (OH), F (Wulser¨ et al. [10]). These minerals are isostructural, crystallizing in the trigonal theMuseum(whostoredthemwithalabel“manaccanite,” system, space group R-3, with lattices a =10.28−10.576 Aand˚ a Mg-rich variety of ilmenite), and the original catalogue c =20.52−21.325 A,˚ and they present a great variability of number, M/U 13524, were newly found (Figure 1). composition (only Ti and Fe are systematically present). Two small crystals were analysed in the laboratory of the Department of Earth Science of the University of Turin 3. Material and Methods and of the CrisDi (Interdepartmental Centre for the Research and Development of Crystallography, Turin, Italy) for the The choice of analytical methods was oriented on nonde- identification. structive analyses, due to the scarcity, the small dimensions, The analyses demonstrate that the old specimens are and the historical relevance of the samples. dessauite-(Y) (Orlandi et al. [8]). The chemical composition was obtained with semiquanti- Dessauite-(Y) is a rare member of the crichtonite super- tative, nondestructive EDS microanalysis, for determination group and occurs as few millimetres flattened rhombohedral of major and minor elements; microRaman spectroscopy was crystals, tabular {001} with hexagonal outline, black or used for identification purposes and spectrum collection. blackish brown in colour, and metallic up to subadamantine Crystallographic data were achieved by X-ray diffraction. lustre. EDS data were acquired by SEM-EDS analysis using a This paper deals with clarifying the identification of his- Cambridge Stereoscan 360 Scanning Electron Microscope, torical samples, rediscovered after many years, using modern equipped with an Oxford Inca Energy 200 EDS Micro- analytical techniques, and it gives additional information analysis, Pentafet detector, and ultrathin window for the on known mineral species, such as the Raman spectrum of determination of elements with Z number down to boron. dessauite-(Y) and gramaccioliite-(Y) (Orlandi et al. [9]), until All the spectra were obtained at 15 kV accelerating voltage, now never published. In addition, it is interesting to outline 25 mm working distance, and 1 A probe current, for time that the occurrence of dessauite-(Y) in La Beaume (Oulx, comprising between 60 and 300 seconds. Primary stan- Susa Valley, Piedmont, Italy) represents the first probed dardizationwasperformedonSPISuppliesandPolaron International Journal of Mineralogy 3 Equipment analytical standards and daily standardization performedonhighpuritymetalliccobaltstandard.Agood quantitative analysis usually requires a very flat and polished surface, but this could have been obtained only by causing the destruction of the sample. So a small crystal was instead gluedoncarbonconductivetapeandgraphitizedforanaly- sis. X-ray powder and single-crystal diffraction studies were carried out using an Oxford Gemini R Ultra diffractometer equipped with a CCD area detector at CrisDi (Interde- partmental Centre for the Research and Development of Crystallography, Torino, Italy). Graphite-monochromatized 1 mm MoK radiation ( =0.71073A)˚ was used. Unpolarized microRaman spectra were obtained on an Figure 2: One of the two crystals investigated by Colomba, found unpolishedcrystalwithaJobin-YvonHoribamodelLabRam in the old material of the Regional Museum and used for the EDS HRVIS, using a motorized x-y stage and an Olympus micro- analysis. scopewitha50xobjective. The backscattered Raman signal was collected with 50x objective and the Raman spectrum was obtained for a nonori- ented crystal. The 632.8 nm line of a He-Ne laser was used as excitation; laser power was controlled by means of a series of density filters. The minimum lateral and depth resolution was set to few m. The system was calibrated using the −1 520.6 cm Raman band of silicon before each experimental Spectrum 4 session. The spectra were collected with multiple acquisitions (2 to 6) with single counting times ranging between 20 Spectrum 3 and 120 seconds. Spectral manipulation such as baseline Spectrum 2 adjustment, smoothing, and normalization were performed Spectrum 1 using the Labspec 5 software package. Band component analysis was undertaken using the Fityk software package (Wojdyr [11]), which enabled the type of fitting function to be selected and allows specific parameters to be fixed or varied accordingly.