Eur. J. Mineral. 2019, 31, 823–836 Published online 14 June 2019 To Christian Chopin, for 30 years of dedicated service to EJM Fluorcarmoite-(BaNa), the first Mg-dominant mineral of the arrojadite group Fernando CÁMARA1,*, Erica BITTARELLO2, Marco E. CIRIOTTI3, Fabrizio NESTOLA4, Francesco RADICA5, Federico MASSIMI6 and Roberto BRACCO7 1 Dipartimento di Scienze della Terra “A. Desio”, Università degli Studi di Milano, Via Mangiagalli 34, 20133 Milano, Italy *Corresponding author, e-mail: fernando.camara@unimi.it 2 SpectraLab s.r.l. – Spin-off accademico dell’Università degli Studi di Torino, Frazione Cappellazzo 84, 12062 Cherasco (CN), Italy 3 Associazione Micromineralogica Italiana, Via San Pietro 55, 10073 Devesi-Cirié, Torino, Italy 4 Dipartimento di Geoscienze, Università degli Studi di Padova, Via Giovanni Gradenigo 6, 35131 Padova, Italy 5 Dipartimento di Scienze, Università degli Studi Roma Tre, largo San Leonardo Murialdo 1, 00146 Roma, Italy 6 Dipartimento di Ingegneria Meccanica e Industriale, Università degli Studi Roma Tre, Via della Vasca Navale 79, 00146 Roma, Italy 7 Associazione Micromineralogica Italiana, Via Montenotte18/6, 17100, Savona, Italy Abstract: Fluorcarmoite-(BaNa), ideally A1BaA2h B1,2NaNa1,2Na2Na3hCaCaMMg13Al(PO4)11(PO3OH)WF2, was found in a pebble of the riverbed of the upper Maremola Creek, close to the village of Isallo, in the Magliolo municipality (Savona, Liguria, Italy). The root-name is after Monte Carmo di Loano, the highest peak in the area, namesake of the tectonic unit where the mineral was found and the first locality where phosphate mineralization has been found in the region. The mineral is associated with quartz and almandine and has microscopic inclusions of fluorapatite and possible graftonite. It occurs as yellow–orange and translucent crystals in an anhedral centimetric nodule embedded in quartz. Fluorcarmoite-(BaNa) is brittle, and no cleavage or parting was observed. It has a yellow–orange streak, a vitreous lustre, does not fluoresce under shortwave or longwave ultraviolet light and is weakly pleochroic (light yellow). Fluorcarmoite-(BaNa) is optically biaxial positive, with a = 1.6240(5), b = 1.6255(5), c = 1.6384(5) (589 nm), 2Vmeas = 35(2)° and 2Vcalc = 37.9°. Raman spectroscopy shows the presence of weak bands in the OH-stretching region. The average chemical composition is (wt%, wavelength-dispersive-mode electron microprobe): Na2O 5.83, K2O 0.36, CaO 2.64, SrO 0.46, BaO 7.12, MnO 2.01, FeO 17.68, MgO 15.12, Al2O3 2.57, P2O5 44.96, F 2.14, –O = F2 0.90, H2Ocalc 0.33, total 100.32. The empirical formula calculated on the basis of 50 O + F + (OH) atoms per formula unit (apfu), is: (Na3.77Ca0.94Ba0.93 2þ K0.15Sr0.09h0.12)R=6.00(Mg7.52Fe2þ 4:93 Mn0:57 )R=13.02Al1.01(PO4)11(PO3)(OH0.74F0.26)F2. Strongest lines in the X-ray powder diffraction 4, 2.735 (32) 60 2, 2.682 (39) 226, 2.526 pattern are [d in Å (Icalc) hkl]: 4.959 (25) 020, 4.524 (20) 114, 3.188 (28) 206, 3.012 (100) 42 (25) 424. The crystal structure has been refined using single-crystal X-ray diffractometer data (Rint = 4.1%) in space group Cc (no. 14) to R1 = 0.0342 for 11 511 reflections with Fo > 4r|F| and 0.0417 for all 13 232 data. Refined unit-cell parameters are: a = 16.4013(3) Å, b = 9.9487(1) Å, c = 24.4536(8) Å, b = 105.725(2)°, V = 3840.80(15) Å3 (Z = 4). Fluorcarmoite-(BaNa) is the first Mg-dominant mineral of the arrojadite group. Mg orders preferentially in the M1, M2b, M3a,b, M4a,b and M7a,b sites whereas the non-dominant Fe2+ and very minor Mn2+ show site preference for M2a, M5a,b and M6a,b. The A1 site is mostly populated by Ba, the A2 site is empty, and minor Fe2+ occurs at the B1b site. A significant, but not dominant occupancy of the Na3 site by Na is also observed. Only Ca and Al are present at the Ca and Al sites, respectively. The type material is deposited in the mineralogical collection of the Museo Regionale di Scienze Naturali di Torino, Sezione di Mineralogia, Petrografia e Geologia, Torino (Italy). The mineral and its name have been approved by the IMA-CNMNC (2015-062). Key-words: arrojadite-group minerals; fluorcarmoite-(BaNa); crystal structure, new mineral; new mineral; phosphate; Monte Carmo; Italy. 1. Introduction Arrojadite-group minerals occur typically as primary minerals in granitic pegmatites. They are frequent in Lithium–Cesium–Tantalum (LCT) pegmatites belonging to the beryl-“columbite”-phosphate subtype (in the classification of Černý & Ercit, 2005), e.g. Eagle et al. (2015), https://doi.org/10.1127/ejm/2019/0031-2868 Vignola et al. (2016) and Birch (2018). Arrojadite-group minerals occur also associated with quartz related to hydrothermal activity accompanying a high-phosphorus, extremely fractionated topaz–“zinnwaldite” leucogranite in the Gemerská Poloma area (Košice Region, Slovak Republic; Števko et al., 2015, 2018). Arrojadite-group minerals are also reported in sedimentary rocks, as in northwestern 0935-1221/19/0031-2868 $ 6.30 Ó 2019 E. Schweizerbart’sche Verlagsbuchhandlung, 70176 Stuttgart, Germany Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/31/4/823/4840137/ejm_31_4_0823_0836_camara_2868_online.pdf by UNIVERSITA DEGLI STUDI DI MILANO user 824 F. Cámara et al. Yukon Territory, Canada (Robertson, 1982; Young & Robertson, 1984; Robinson et al., 1992; Tomes et al., 2018), although this is a unique locality. The space group of dickinsonite was given by Wolfe (1941) as C2/c. The space group C2/m was chosen for arrojadite from the Nickel Plate mine (South Dakota, USA) by Lindberg (1950) and later as A21/n by Fisher (1965). The structure of arrojadite-group minerals was first determined on a sample from the Nickel Plate mine (Keystone, South Dakota) by Krutik et al. (1979) using the space group B2/b, a further choice of the space group 15 by Merlino et al. (1981) as C2/c, Moore et al. (1981) as A2/a and Demartin et al. (1996) as C2/c. The crystal-chemistry of the arrojadite group was reinvestigated by Cámara et al. (2006) and Chopin et al. (2006), who described the structure in the non-centrosymmetric space group Cc and established a new classification scheme for the group based on the general formula A2B2CaNa2+x M13Al(PO4)11(PO3OH1–x)W2, where: A corresponds to large divalent cations (Ba, Sr, Pb) or monovalent cations (K, Na) (A1 site), and to monovalent cations (Na) or vacancies (A2 site); B corresponds to small divalent cations (Fe, Mn, Mg at the B1b and B1c sites) and vacancies or monovalent Na cations (at the B1 and B2 sites); Ca is dominant (with minor Sr) at the Ca site; Na is dominant at the Na1 and Na2 sites; Na can also occupy the site Na3 if the third proton bonded to the acid phosphate group is not present (x = 1); M sites contain small divalent cations (Fe2+, Mn2+ and Mg, with minor Li and Zn); the Al site can host Fe3+ and very minor amounts of Ti and Sc; the W site may be occupied by OH or F. The mineral species of the group are then named by a root name plus three suffixes written within parentheses as extended Levinson modifiers and eventual prefixes. The root name is defined by the dominant divalent cation at the M sites: arrojadite (Fe), dickinsonite (Mn), and in case of Mg dominance at M sites, a further root-name was foreseen by Chopin et al. (2006). Regarding suffixes, following the rule of the dominant species of the dominant valence state, the first regards the dominance at the A1 site (once Ca sites have been filled by Ca and divalent cations of increasing radius; the second is based on the occupancy of B sites, which will depend on the excess at the M sites (MFe* = Fe2+ + Mn2+ + Mg + Zn + Li 13 = RM2+ + Li 13), and will be the dominant cation at the M sites or Na in the case that MFe*  0.5 pfu; the third suffix is used when x in the above formula is >0.5, meaning that the proton of the acid phosphate group is substituted by another ion (usually Na). Regarding prefixes, these are used when there is an anion substitution at the W sites (for instance, “fluor” if (OH) is substituted by F) and/or if there is a substitution of Al by Fe3+ at the Al sites. After the classification of Chopin et al. (2006), two further members of the arrojadite group have been described: arrojadite-(BaNa) (Vignola et al., 2016) and fluorarrojadite-(BaNa) (Števko et al., 2018). Fluorcarmoite-(BaNa) is the first arrojadite-group mineral in which Mg is dominant at the M sites. Therefore, because Mg > Fe and >Mn, a new root name is warranted according to the nomenclature of the arrojadite group (Chopin et al., 2006). The new root-name is after Monte Carmo di Loano (Savona, Liguria, Italy), the locality where the sample was found. Monte Carmo is the highest peak in the area, and the first locality where phosphate mineralization was found in the region. The prefix “fluor” and suffix -(BaNa) follow the rules in Chopin et al. (2006), with an ideal formula A1 A2 B1,2 Ba h NaNa1,2Na2Na3hCaCaMMg13Al(PO4)11(PO3OH)WF2 and charge arrangement #3 of Chopin et al. (2006). The new mineral was approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (IMA 2015-062). A fragment of the holotype material is deposited in the mineralogical collection of the Museo Regionale di Scienze Naturali di Torino, Sezione di Mineralogia, Petrografia e Geologia, via Giovanni Giolitti 36, I-10123 Torino (Italy), catalogue number M/15940. 2. Geological setting and mineral occurrence The mineral occurs in the riverbed of the upper Maremola Creek, close to the village of Isallo, in the Magliolo municipality (Savona, Liguria, Italy; ~44°110 3700 N, ~8° 150 100 E). The locality is also known by mineral collectors as “Costa Balzi Rossi”, after the overlying cliff where rich associations of rare-earth minerals have been found in recent years. The Monte Carmo tectonic unit of the Briançonnais domain crops out in the area and includes a Permian metavolcanic basement (“Scisti di Gorra” schists, “Porfiroidi del Melogno” ignimbrites, “Formazione di Eze” volcanic ash), followed by a Permo-Triassic cover starting with polygenic conglomerates (“Verrucano Brianzonese”) and sedimentary quartzites (“Quarziti di Ponte di Nava”), underlying younger carbonate sequences. Fluorcarmoite-(BaNa) was found in an erratic rounded pebble in the riverbed of the Maremola Creek by one of the authors (RB) in 2012. The erratic pebble is related to phosphate-bearing quartzites occurring in the area, especially on nearby Monte Carmo di Loano (Boiteau, 1971; Cortesogno, 1984; Menardi Noguera, 1984; Cortesogno et al., 1987; Bracco & Marchesini, 2016), which in turn are part of a thick horizon of quartzites sparsely occurring all over the Alpine range. The origin of phosphate mineralization is uncertain. At the Monte Carmo di Loano site, as well as most other Alpine localities, lazulite is the most widespread phosphate, but several less common phosphates have been reported (Bracco et al., 2007; Bracco & Marchesini, 2016). The mineral is associated with quartz and almandine and has microscopic inclusions of fluorapatite and possible graftonite. Other minerals found at the same locality, but not associated with fluorcarmoite-(BaNa), are: “adularia”, aeschynite-(Y), albite, allanite-(Ce), anatase, bastnäsite(Ce), brookite, cassiterite, cerussite, chernovite-(Y), churchite-(Y), clinochlore, fergusonite-(Y), gorceixite, goyazite, graftonite, hematite, hingganite-(Y), hundolmenite(Y), jarosite, lazulite, magnetite, mitridatite, monazite-(Ce), Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/31/4/823/4840137/ejm_31_4_0823_0836_camara_2868_online.pdf by UNIVERSITA DEGLI STUDI DI MILANO user Fluorcarmoite-(BaNa), the first Mg-dominant mineral of the arrojadite group 825 monazite-(La), paraniite-(Y), pyrite, pyrrothite, rhabdophane-(Nd), rutile, schorl–dravite tourmaline series, thortveitite, titanite, wulfenite and xenotime-(Y) (Bracco et al., 2006, 2007, 2009, 2012; Castellaro, 2014; Bracco & Marchesini, 2016). Fluorcarmoite-(BaNa), except for minor fluorapatite and possible graftonite inclusions, is the main phosphate observed in the type specimen and occurs as an anhedral centimetric nodule embedded in quartz, presumably syngenetic. Another arrojaditic phosphate of a different composition is associated with fluorcarmoite-(BaNa), but its volume is very small, and it will probably be impossible to characterize it. Its composition is much richer in Ca. The occurrence strongly resembles that of the type locality of arrojadite-(BaFe) at Alpe Groppera in the Central Alps, Sondrio Province, Lombardy, Italy (Demartin et al., 1996; Cámara et al., 2006; Chopin et al., 2006). 3. Appearance and physical properties Fluorcarmoite-(BaNa) occurs as subhedral equant crystals, stout, more or less platy prisms 10–15 mm in size (Fig. 1) on compact quartz. The mineral is brittle, and no cleavage or parting was observed. Elastic modulus and hardness were measured with a Nano Indenter Agilent G200 in CSM mode (Continuous Stiffness Measurement; Oliver & Pharr 1992, 2004), with a frequency of 45 Hz, amplitude of oscillation 2 nm, constant strain rate of 0.05 s 1; the range of displacement into surface for the average values elastic modulus and hardness is 50–100 nm. Results of hardness and modulus profiles are: elastic modulus 147 ± 3.6 (GPa), hardness 12.12 ± 0.47 (GPa), Vickers hardness 1236, Mohs > 7 < 8. These values were obtained after averaging over five different tests. The Poisson’s ratio is assumed to be 0.2. Before and after the tests on the samples, tests on a standard sample of silica were done to calibrate the instrument. Fluorcarmoite-(BaNa) has a yellow–orange streak, a vitreous lustre and does not fluoresce under shortwave or longwave ultraviolet light. Individual crystals are yellow– orange in colour and translucent. Fluorcarmoite-(BaNa) is optically biaxial positive, with a 2Vmeas = 35(2)° (program ExcalibrW was used to process the extinction data and to determine the 2V value; Gunter et al., 2005) and 2Vcalc = 37.9°. The measured refractive indices are a = 1.6240(5), b = 1.6255(5), c = 1.6384(5) (589 nm). Refractive indices were determined by the double-variation method (Su et al., 1987; Gunter et al., 2005) using standard Cargille liquids as reference. Fluorcarmoite-(BaNa) is weakly pleochroic (light yellow to colourless). Fluorcarmoite-(BaNa) is unreactive and insoluble in either 2 M HCl, 10% HCl or 65% HNO3. The measured density of is 3.40 g/cm3 (Clerici solution). The calculated density obtained from the empirical formula and unit-cell parameters of the single crystal used for the crystal-structure determination is 3.394 g/cm3. The mean refractive index n of fluorcarmoite-(BaNa), the calculated density and the empirical formula obtained by electron microprobe (see below) Fig. 1. Photograph of fluorcarmoite-(BaNa). Collection and photo R. Bracco (field of view 25 mm). yielded a Gladstone-Dale compatibility index (Mandarino, 2007) of 0.020, rated as excellent. 4. Chemical data 4.1. Electron microprobe The chemical composition was determined using a Cameca SX-50 electron microprobe operated in wavelengthdispersive (WDS) mode at CNR-IGG of Padova (installed at Department of Geosciences of University of Padova) on grains extracted from the holotype, close to the place where the crystal used for the diffraction study was extracted, embedded in epoxy resin and polished. Major and minor elements were determined at 15 kV accelerating voltage and 10 nA beam current (beam size 3 lm), with 40–20 s count time on both peak and background. Probe standards (spectral line; analysing crystal) were: Amelia albite (NaKa; TAP), orthoclase (KKa; PET), diopside (CaKa; PET), celestine (SrLa; PET), baryte (BaLa; LIF), MnTiO3 (MnKa; LiF), Fe2O3 (FeKa; LiF), MgO (MgKa; TAP), Al2O3 (AlKa; TAP), apatite (PKa; TAP), fluorite (FKa; TAP). X-ray counts were converted to oxide wt% using the PAP correction program (Pouchou & Pichoir, 1984, 1985). The crystals selected for study are compositionally homogeneous. Only sporadic inclusions of fluorapatite and possible graftonite were found in the sample. H2O was calculated on the basis of 3(OH) + F groups pfu (Chopin et al., 2006). The average of 15 analyses is given in Table 1. The amount of P2O5 analysed is higher than expected for 12 P apfu. In fact, the normalized values lead to 12.27 P apfu. This can be due just to intrinsic uncertainty that in the case of ca. 2% in P stoichiometry converts into 1.35 charge, i.e., more than a complete heterovalent substitution on any site. As a matter of fact these deviations from the ideal P content affect low-charge cation contents in a way that may prevent a correct classification (Chopin et al., 2006). In the case of normalization to 12 P pfu (and H by charge balance), the Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/31/4/823/4840137/ejm_31_4_0823_0836_camara_2868_online.pdf 826 F. Cámara et al. Table 1. Analytical data (wt%) for fluorcarmoite-(BaNa) (15 analytical points). Na2O K2O CaO SrO BaO MnO FeO MgO Al2O3 P2O5 F Subtotal OF H2O** Total P2O5* Mean Range SD 5.83 0.36 2.64 0.46 7.12 2.01 17.68 15.12 2.57 44.96 2.14 100.89 0.90 0.33 100.32 42.53 5.48–6.18 0.30–0.45 2.53–2.79 0.20–0.64 6.14–8.07 1.69–2.33 16.90–18.09 14.84–15.46 2.48–2.76 43.51–45.29 2.02–2.29 98.10–102.18 0.85–0.97 0.27–0.40 96.26–101.65 41.77–43.05 0.16 0.05 0.08 0.13 0.55 0.18 0.29 0.19 0.09 0.42 0.00 0.98 0.03 0.04 1.43 0.37 *Reduced to the 95% to obtain 12 P apfu following recommendations in Chopin et al. (2006), see text. **By stoichiometry. effect of small P errors on the sums of cations, and therefore on the number of vacancies, is amplified. Normalization using the analysed value produces a sum of M sites (Fe2+ + Mn2+ + Mg) of 12.58 apfu. Whereas this could be in agreement with the observed light site scattering at M sites (see structure refinements results ahead), it would imply no Fe2+ left to be partitioned in B1 sites, in contrast with results from refinement. Therefore, following recommendation by Chopin et al. (2006), a lower value of P2O5 was calculated and used to calculate the normalized mean analysis. Calculated value is reported in Table 1. The empirical formula calculated on the basis of 50 O + F+(OH) apfu is then: (Na3.77Ca0.94 Ba 0.93 K0.15 Sr 0.09 h0.12) R=6.00(Mg 7.52 Fe2þ 4:93 Mn2þ The 0:57 )R=13.02 Al1.01 (PO4 )11 (PO3 )(OH0.74 F0.26 )F2 . simplified formula is BaNa4CaMg13Al[(PO4)11(OH)(PO3)] F2, which requires Na2O 6.92, BaO 8.56, CaO 3.13, MgO 29.26, Al2O3 2.85, P2O5 47.55, F 2.12, H2O 0.50, total 100 wt%. 5. Micro-Raman spectroscopy The Raman spectrum of fluorcarmoite-(BaNa) (Fig. 2) was obtained using a micro/macro Jobin Yvon Model LabRam HRVIS, equipped with a motorized x–y stage and an Olympus microscope. The backscattered Raman signal was collected with a 50 objective and the Raman spectrum was obtained for a randomly oriented crystal. The 632.8 nm line of a He–Ne laser was used as excitation; laser power was controlled by density filters. The minimum lateral and depth resolution was set to a few lm. The system was calibrated using the 520.6 cm 1 Raman band of silicon before each experimental session. The spectra were collected with multiple acquisitions (2–6) with single counting times ranging between 20 and 180 s. Spectral manipulation such as baseline adjustment, smoothing and normalization were done using the LabSpec 5 software package (Horiba Jobin Yvon GmbH, 2004, 2005). After background removal, band-component analysis was done using the Fityk software package (Wojdyr, 2010), which enabled the type of fitting function to be selected and allows specific parameters to be fixed or varied accordingly. 6. X-ray diffraction Experimental X-ray powder diffraction data were collected using an Oxford Gemini R Ultra diffractometer equipped Fig. 2. Raman spectrum of fluorcarmoite-(BaNa) over the 100–4000 cm 1 range. Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/31/4/823/4840137/ejm_31_4_0823_0836_camara_2868_online.pdf by UNIVERSITA DEGLI STUDI DI MILANO user Fluorcarmoite-(BaNa), the first Mg-dominant mineral of the arrojadite group Table 2. X-ray powder diffraction data for fluorcarmoite-(BaNa).* h k 1 0 3 0 1 2 1 3 2 2 4 3 3 3 1 4 6 2 1 0 4 0 7 6 1 2 1 2 1 2 1 1 0 2 2 3 1 3 3 0 0 2 3 2 2 4 1 4 l 4 0 2 2 4 2 6 4 6 6 4 2 8 0 4 8 2 6 6 8 4 0 6 2 dobs (Å) dcalc (Å) 5.182 4.959 4.733 4.570 4.524 4.150 3.374 3.289 3.188 3.097 3.012 2.818 2.808 2.801 2.772 2.742 2.735 2.682 2.567 2.530 2.526 2.480 2.182 1.837 5.188 4.974 4.731 4.582 4.526 4.158 3.374 3.286 3.186 3.102 3.013 2.823 2.809 2.806 2.777 2.742 2.730 2.683 2.572 2.533 2.525 2.487 2.180 1.839 Iobs Icalc 11.2 24.8 12.9 23.8 19.9 21.7 17.0 10.0 27.5 19.6 100.0 28.4 17.2 12.7 9.9 19.8 32.1 39.2 11.0 9.2 24.9 9.9 11.8 7.0 6.3 26.1 7.3 15.6 25.1 22.4 22.8 20.2 40.3 12.3 100.0 20.0 16.9 11.9 9.4 20.1 27.3 40.3 13.8 16.4 26.5 19.5 12.6 5.5 *Only reflections with Irel > 7r(Irel) are listed. The seven strongest reflections are reported in bold. with a CCD area detector at CrisDi (Interdepartmental Centre for the Research and Development of Crystallography, Torino, Italy) with graphite-monochromatized MoKa radiation. The unit-cell parameters refined from the powder data with the software GSAS (Larson & Von Dreele, 1994) are: a = 16.426(9), b = 9.920(8), c = 24.43(3) Å, b = 105.65 (11)°, V = 3832(6) Å3, Z = 4. Fluorcarmoite-(BaNa) is monoclinic, space group Cc. Observed d-spacings and diffraction intensities for MoKa radiation are compared with those calculated from the structure model using PLATON v-140513 (Spek, 2009) and are reported in Table 2. Single-crystal X-ray diffraction data were collected on a crystal of 0.200  0.133  0.110 mm using an Oxford Xcalibur Gemini Ultra diffractometer equipped with a Ruby CCD area detector at CrisDi with graphitemonochromatised MoKa radiation (k = 0.71073 Å). No crystal twinning was observed. Crystal data and experimental details are reported in Table 3. The intensities of 48 640 reflections with 24  h  23, 15  k  14, 36  l  37 were collected to 65.5° 2h using a 1° frame and an integration time of 42 s. Data were integrated and corrected for Lorentz and polarization background effects using the package CrysAlisPro (Agilent Technologies, Version 1.171.36.28, release 01-02-2013 CrysAlis171). Data were corrected for empirical absorption using spherical harmonics, implemented in the SCALE3 ABSPACK scaling algorithm in CrysAlisPro. Refinement of the unit-cell parameters was based on 21 512 measured reflections with I > 10r(I). At room temperature, the unit-cell parameters are: a = 16.4013(3), b = 9.9487(1), c = 24.4536(8) Å; 827 Table 3. Crystal data and summary of parameters describing data collection and refinement for fluorcarmoite-(BaNa). Crystal system Space group Unit-cell dimensions a (Å) b (Å) c (Å) b (°) V (Å3) Z F(000) Dcalc (g cm 3) Crystal size (mm) Radiation type h-range for data collection (°) Rint (%) Reflections collected Independent reflections Fo > 4r|F| Refinement method No. of refined parameters Final Robs (%) all data R1 (%) Fo > 4r|F| wR2 (%) Fo > 4r|F| Highest peak/deepest hole (e Å 3) Goodness of fit on F2 Monoclinic Cc 16.4013 (3) 9.9487 (1) 24.4536 (8) 105.725 (2) 3840.80 (15) 4 3616 3.394 0.200  0.133  0.110 MoKa (0.71073 Å) 3.2–32.7 4.1 48 778 13 232 11 511 Least-squares, full matrix 847 4.17 3.42 8.77 1.32/ 1.02 1.040 b = 105.725(2)°, V = 3840.80(15) Å3, Z = 4, space group Cc and Z = 4. The a:b:c ratio is 1.6486:1:2.4580. The structure was refined starting from the atom coordinates of arrojadite-(KNa) (Cámara et al., 2006) using the SHELX set of programs (Sheldrick, 2008). Structure refinement converged to R1 = 0.0342 for 11 511 reflections with Fo > 4r|F| and 0.0417 for all 13 232 data. Table 4 reports atomic coordinates. Table S1 with anisotropic-displacement parameters is deposited and available as Supplementary Material linked to this article at https://pubs.geoscienceworld.org/eurjmin. Tables 5–7 report selected bond distances, geometrical parameters and bond valence for fluorcarmoite-(BaNa). Site scattering values and site occupancies are reported in Table 8. The CIF and structure factor list are available as part of the Supplementary Material. 7. Results 7.1. Raman spectroscopy The Raman spectrum of fluorcarmoite-(BaNa) from 100 to 4000 cm 1 is reported in Fig. 2. The spectral region between 100 and 700 cm 1 includes the phosphate bending modes (PO4 and PO3(OH) bending vibrations). Quite intense bands are found at 141, 162, 199 and 253 cm 1 and these bands may be simply described as lattice vibrations of phosphate groups. A series of broad bands are observed at 441, 452, 553, 580, 639 cm 1 and these bands are attributed to motions of cations at the M sites. The Raman spectrum, in the region of 700–1400 cm 1, shows a number of overlapping bands. Intense Raman bands Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/31/4/823/4840137/ejm_31_4_0823_0836_camara_2868_online.pdf by UNIVERSITA DEGLI STUDI DI MILANO user 828 F. Cámara et al. Table 4. Atoms, site occupancy (cation sites)/bond valence (B.V., anion sites, valence units, v.u.), fractional atom coordinates (Å), and equivalent isotropic displacement parameters (Å2) for fluorcarmoite-(BaNa). Site occupancy/B.V. A1 A2 B1 B1b B2 B2b Na1 Na2 Na3 Na3x Caa Cab M1 M2a M2b M3a M3b M4a M4b M5a M5b M6a M6b M7a M7b Al P1 P10 P1b P1b0 P2a P2b P3a P3b P4a P4b P5a P5b P6a P6b O1a O1b O2a O2b O3a O3b0 O3bx O4a O4x O5a 2+ 0.964(1) Ba h 0.341(4) Na+ 0.305(4) Fe2+ 0.776(10) Na+ 0.224(10) Na+ 0.957(7) Na+ 0.902(10) Na+ 0.189(13) Na+ 0.490(14) Na+ 0.476(11) Ca2+ 0.524(11) Ca2+ 0.901(10) Mg2+ 0.099(10) Fe2+ 0.415(11) Mg2+ 0.585(11) Fe2+ 0.608(11) Mg2+ 0.392(11) Fe2+ 0.948(13) Mg2+ 0.853(11) Mg2+ 0.147(11) Fe2+ 0.784(9) Mg2+ 0.216(9) Fe2+ 0.731(9) Mg2+ 0.269(9) Fe2+ 0.409(9) Mg2+ 0.591(9) Fe2+ 0.487(9) Mg2+ 0.513(9) Fe2+ 0.335(10) Mg2+ 0.665(10) Fe2+ 0.456(10) Mg2+ 0.544(10) Fe2+ 0.634(9) Mg2+ 0.366(9) Fe2+ 0.635(10) Mg2+ 0.365(10) Fe2+ 0.974(5) Al3+ 0.683(6) P 0.317(6) P 0.341(4) P 0.659(4) P 1P 1P 1P 1P 1P 1P 1P 1P 1P 1P 1 O/1.91 1 O/1.94 1 O/2.00 1 O/1.91 1 O/2.24 0.659(4) O/1.14 0.341(4) O/0.46 1 O/1.63 1 O/1.93 1 O/2.08 x y z 0.00061(6) 0.50259(2) 0.24760(4) 0.0196(1) 0.2963(3) 0.27827(17) 0.1330(3) 0.1722(8) 0.0001(4) 0.1365(4) 0.503(4) 0.5117(8) 0.2301(3) 0.2647(3) 0.22094(19) 0.5457(5) 0.6095(2) 0.4809(4) 0.4809(11) 0.0004(5) 0.5184(4) 0.434(2) 0.5265(10) 0.2164(4) 0.2739(4) 0.8968(3) 0.04276(17) 0.01984(10) 0.11904(18) 0.1085(5) 0.0019(2) 0.12220(18) 0.251(2) 0.2572(5) 0.01924(19) 0.0099(2) 0.02817(14) 0.005* 0.0039(6)* 0.0212(10) 0.025* 0.0256(5) 0.0436(18) 0.087(8)* 0.080(4)* 0.0196(12) 0.0323(18) 0.0402(10) 0.48449(15) 0.23009(7) 0.0154(5) 0.28937(11) Ueq 0.28804(12) 0.51569(16) 0.23472(7) 0.0099(5) 0.10801(18) 0.10671(17) 0.0172(2) 1.0161(2) 0.13771(11) 0.14227(10) 0.0061(7) 0.0139(7) 0.02111(14) 0.25170(19) 0.09941(8) 0.0101(6) 0.02022(13) 0.74906(19) 0.09528(8) 0.0121(6) 0.03343(9) 0.25408(14) 0.09790(6) 0.0118(4) 0.03480(9) 0.74488(15) 0.10222(6) 0.0087(4) 0.20437(10) 0.70445(16) 0.15000(6) 0.0163(5) 0.29668(10) 0.79640(16) 0.14510(6) 0.0128(5) 0.28167(12) 0.2057(2) 0.15412(7) 0.0139(5) 0.21956(12) 0.7051(2) 0.34102(7) 0.0154(6) 0.0008(2) 0.1147(2) 0.0813(4) 0.4199(4) 0.3860(2) 0.13074(13) 0.12912(13) 0.12832(12) 0.37395(13) 0.10290(13) 0.10175(12) 0.12927(12) 0.12978(13) 0.14374(13) 0.14466(12) 0.4762(4) 0.0258(3) 0.3906(4) 0.1107(4) 0.3576(5) 0.3204(4) 0.4705(6) 0.1813(5) 0.3478(3) 0.0512(3) 0.5006 1.0122(3) 1.0027(6) 0.4987(5) 0.4873(3) 0.4654(2) 0.53436(19) 0.74790(18) 0.75144(18) 0.23166(19) 0.76840(19) 0.72937(18) 0.27178(18) 0.30126(19) 0.69881(17) 0.4312(5) 0.0676(5) 0.6368(5) 0.8612(5) 0.5772(6) 0.4535(6) 0.5264(8) 1.0365(8) 0.4139(5) 0.4413(5) Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/31/4/823/4840137/ejm_31_4_0823_0836_camara_2868_online.pdf 0.00249(14) 0.0067(2) 0.13417(13) 0.0099(4) 0.1677(3) 0.0113(14)* 0.1621(3) 0.0104(12) 0.12899(14) 0.012* 0.07934(8) 0.0105(3) 0.07444(8) 0.0102(3) 0.03701(7) 0.0087(3) 0.04174(7) 0.0088(3) 0.04659(7) 0.0101(3) 0.05087(8) 0.0096(3) 0.21506(7) 0.0087(3) 0.21020(8) 0.0110(3) 0.20779(8) 0.0118(4) 0.20344(8) 0.0093(3) 0.1302(2) 0.0148(10) 0.1344(2) 0.0144(10) 0.1347(3) 0.0171(11) 0.1400(3) 0.0156(11) 0.1802(3) 0.050(2) 0.0725(2) 0.013* 0.2220(4) 0.0104(15)* 0.0777(4) 0.080(2) 0.1711(2) 0.0175(9) 0.0572(2) 0.0107(10) (Continued on next page) Fluorcarmoite-(BaNa), the first Mg-dominant mineral of the arrojadite group 829 Table 4. (Continued) Site occupancy/B.V. O5b O6a O6b O7a O7b O8a O8b O9a O9b O10a O10b O11a O11b O12a O12b O13a O13b O14a O14b O15a O15b O16a O16b O17a O17b O18a O18b O19a O19b O20a O20b O21a O21b O22a O22b O23a O23b O24a O24b W1 W2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 O/2.10 O/1.94 O/2.05 O/1.99 O/1.95 O/2.00 O/2.02 O/1.96 O/2.09 O/2.05 O/1.96 O/2.03 O/1.92 O/1.85 O/1.97 O/2.12 O/1.95 O/2.12 O/2.14 O/1.91 O/1.94 O/2.09 O/1.89 O/1.96 O/1.99 O/1.97 O/2.01 O/1.99 O/1.88 O/2.04 O/2.06 O/1.89 O/1.95 O/1.87 O/2.00 O/2.07 O/2.03 O/1.96 O/1.87 F/0.68 F/0.71 x y z Ueq 0.0492(4) 0.1188(4) 0.1188(4) 0.1297(4) 0.3725(4) 0.2107(4) 0.2895(4) 0.0839(4) 0.4141(3) 0.0953(4) 0.0957(3) 0.1096(4) 0.3933(4) 0.2242(4) 0.2759(4) 0.0445(3) 0.0460(3) 0.0651(4) 0.0654(3) 0.0951(4) 0.0959(4) 0.1937(4) 0.1949(3) 0.0481(3) 0.0487(4) 0.1330(4) 0.1322(4) 0.1332(4) 0.1324(4) 0.2063(3) 0.2064(4) 0.0577(3) 0.0614(4) 0.1487(4) 0.1516(4) 0.1493(4) 0.1530 (4) 0.2172(4) 0.2197(4) 0.2314(3) 0.2711(4) 0.5595(5) 0.5985(5) 0.4054(5) 0.3408(5) 0.1573(5) 0.4578(7) 1.0322(5) 0.8319(5) 0.6695(5) 0.6046(5) 0.3982(5) 0.8119(6) 0.6880(5) 0.7459(6) 0.7532(5) 0.3568(5) 0.6445(5) 0.1261(5) 0.8720(5) 0.1840(5) 0.8146(6) 0.2652(5) 0.7356(6) 0.6765(5) 0.3254(6) 0.3242(6) 0.3217(6) 0.8822(5) 0.1155(5) 0.6719(6) 0.3280(5) 0.3462(5) 0.6510(6) 0.6462(6) 0.6463(6) 0.1487(5) 0.8529(5) 0.3620(6) 0.6392(6) 1.0010(5) 0.4906(6) 0.0542(2) 0.1132(3) 0.1071(3) 0.1168(2) 0.1137(2) 0.0314(3) 0.0259(2) 0.0747(2) 0.0794(2) 0.0339(2) 0.0391(2) 0.0225(2) 0.0176(2) 0.0619(2) 0.0660(3) 0.0471(2) 0.0516(2) 0.0791(2) 0.0845(2) 0.0142(2) 0.0090(2) 0.0755(2) 0.0815(2) 0.1738(2) 0.1695(3) 0.2255(2) 0.2693(2) 0.2127(2) 0.2076(2) 0.1976(2) 0.1915(2) 0.1690(2) 0.1635(2) 0.2317(2) 0.2622(2) 0.2066(2) 0.2023(2) 0.1875(3) 0.1823(2) 0.13727(17) 0.1416(3) 0.0115(10) 0.0179(11) 0.0200(12) 0.0133(10) 0.0163(11) 0.0294(14) 0.0174(11) 0.0144(10) 0.0116(9) 0.0142(10) 0.0094(9) 0.0160(11) 0.0148(11) 0.0172(11) 0.0167(11) 0.0122(10) 0.0103(10) 0.0141(11) 0.0124(10) 0.0162(11) 0.0182(12) 0.0167(11) 0.0163(11) 0.0128(10) 0.0172(11) 0.0182(12) 0.0125(10) 0.0219(13) 0.0189(13) 0.0155(11) 0.0172(11) 0.0116(10) 0.0178(11) 0.0205(13) 0.0216(12) 0.0146(10) 0.0175(12) 0.0198(12) 0.0183(12) 0.0238(10) 0.0460(16) *The temperature factor has the form exp( T) where T = 8(p2)U(sin(h)/k)2 for isotropic atoms. are observed at 989 and 964 cm 1 with shoulder bands at 949, 927 and 864 cm 1. These bands are assigned to the PO4 m1 symmetric stretching modes. The Raman band at 989 cm 1 is attributed to the stretching vibrations of PO3(OH) groups. Multiple bands are observed depending upon to which cation the phosphate is bonding. Raman shoulder bands are also observed at 1037, 1063 and 1156 cm 1 and these are assigned to the PO4 m3 antisymmetric stretching modes (Casciani & Condrate, 1980; Frost et al., 2013). In the region of 1800–4000 cm 1: broad bands and weak shoulders are observed. Band component analysis enables resolution with bands at 3011, 3422, 3545, 3586, 3746 and 3913 cm 1 that might be assigned to OH stretching modes. However, the stretching modes described by Cámara et al. (2006), Frost et al. (2013) and Della Ventura et al. (2014) are a doublet centred at ca. 3526 and 3554 cm 1. Weak components at 3100–3200 cm 1 are reported by Frost et al. (2013) and by Della Ventura et al. (2014) and can be interpreted as due to the O3x–H3x bonding (mistakenly reported by Della Ventura et al. (2014) as O25–H3, as O25a,b = W1,2 is not involved in the PO3OH group). The presence of significant scattering at the Na3,3x sites implies that the intensity of that vibration must be weak. It is worth noting that Della Ventura et al. (2014) reported the presence of NH4+ in arrojadite-(KNa) from Rapid Creek (Yukon) by means of WDS microprobe analysis and FTIR, which would show bands related to m3 antisymmetric stretching modes at ca. 3090 cm 1. Additional bending m4 modes at 1400 cm 1 are then expected (found by Della Ventura et al., 2014 at ca. 1450 cm 1). The presence of a weak band at 1529 cm 1 does not support the presence of NH4+ in fluorcarmoite-(BaNa) that could account for the “excess” scattering at the Na3,3x sites (see below). Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/31/4/823/4840137/ejm_31_4_0823_0836_camara_2868_online.pdf by UNIVERSITA DEGLI STUDI DI MILANO user 830 F. Cámara et al. Table 5. The phosphate groups. Main interatomic distances (Å), geometrical parameters and bond valence valuesa (v.u.) for fluorcarmoite(BaNa). P1–O3a –O2b –O4a –O1b <P1–O> Vb (Å3) P10 *–O3a –O1b –O2b <P10 –O> 1.474(7) 1.509(6) 1.529(8) 1.556(6) 1.517 1.78 1.346(9) 1.520(8) 1.580(8) 1.482 0.99 0.91 0.86 0.81 3.57 1.78 0.64 0.42 0.36 1.41 P1b–O3bx –O1a –O4x –O2a <P1b–O> V(Å3) 1.502(11) 1.517(8) 1.517(8) 1.547(7) 1.520 1.79 0.46 0.44 0.44 0.41 1.76 P1b0 –O2a –O4x –O3b0 –O1a <P1b0 –O> V(Å3) 1.495(6) 1.527(6) 1.541(7) 1.574(7) 1.534 1.84 0.91 0.84 0.81 0.75 3.31 P2a–O8a –O7a –O6a –O5a <P2a–O> V(Å3) 1.506(6) 1.538(5) 1.546(5) 1.561(5) 1.538 1.851 1.34 1.24 1.22 1.17 4.97 P3a–O10a –O12a –O11a –O9a <P3a–O> V(Å3) 1.497(6) 1.528(6) 1.542(6) 1.551(5) 1.530 V(Å3) 1.520(5) 1.525(6) 1.540(5) 1.562(6) 1.537 1.86 1.37 1.27 1.23 1.20 5.08 1.83 1.30 1.28 1.23 1.17 4.98 P3b–O9b –O11b –O10b –O12b <P3b–O> V(Å3) 1.509(6) 1.534(6) 1.538(5) 1.557(6) 1.534 1.85 P4a–O16a –O15a –O14a –O13a <P4a–O> V(Å3) P4b–O15b –O14b –O13b –O16b <P4b–O> V(Å3) P2b–O6b –O8b –O5b –O7b <P2b–O> P5b–O18b –O17b –O20b –O19b <P5b–O> V(Å3) 1.524(6) 1.530(5) 1.533(6) 1.550(5) 1.534 V(Å3) 1.520(5) 1.526(6) 1.553(6) 1.557(5) 1.539 1.87 1.28 1.27 1.26 1.20 5.01 1.85 1.30 1.28 1.19 1.18 4.95 1.33 1.25 1.24 1.18 5.01 P6a–O23a –O21a –O24a –O22a <P6a–O> V(Å3) 1.522(5) 1.538(5) 1.546(7) 1.551(5) 1.539 1.87 1.29 1.24 1.22 1.20 4.95 1.503(6) 1.533(6) 1.544(5) 1.573(5) 1.538 1.86 1.35 1.26 1.22 1.14 4.97 P6b–O22b –O21b –O23b –O24b <P6b–O> V(Å3) 1.503(69 1.524(6) 1.540(5) 1.574(6) 1.535 1.85 1.35 1.28 1.23 1.13 5.01 1.512(6) 1.536(6) 1.538(6) 1.543(6) 1.532 1.84 1.32 1.25 1.24 1.23 5.04 P5a–O19a –O17a –O18a –O20a <P5a–O> a Bond-valence parameters from Gagné & Hawthorne (2015) for bond with O= and from Brown (1981) for bonds with F . The fourth oxygen could not be identified in the Fourier-difference map and was not added to the model; bond valence at split sites P1 and P10 and P1b and P1b0 correspond to the partial occupancies at these sites. *V = polyhedral volume. b 7.2. Description of the structure The crystal structure of fluorcarmoite-(Ba,Na) is topologically identical to the structure of arrojadite-(KNa): four-, five- and six coordinated cations are linked by (PO4) groups and Al octahedra sharing apices, except for M4a,b and M5a, b that share an edge with P2a,b and P4a,b, respectively – in fact these cation polyhedra show the highest angle-variance values (r2, Tables 5 and 6) along with P1 sites. Interestingly, site-scattering refinement (Hawthorne et al., 1995) shows the highest scattering for the M5a,b and M6a,b sites, indicating that Fe2+ orders preferentially in these sites (Table 4). From the point of view of the Structure Hierarchy Hypothesis (Hawthorne, 1983, 1994), “structures may be ordered hierarchically according to the polymerization of coordination polyhedra of higher bond valence”. Therefore, higher bond-valence polyhedra polymerize to form homo- or heteropolyhedral clusters; these may be considered as the fundamental building block (FBB) of the structure. The FBB is repeated (often polymerized) by symmetry to form the structural unit, a complex (usually anionic) polyhedral array (not necessarily connected). In the case of arrojadite minerals, we can identify the FBB as the complex polyanion M12O17(OH,F)6½PO4 Š610 (Fig. 3a). It is composed of two elements that repeat twice in the FBB: a folded strip of four edge-sharing octahedra and one edge-sharing PO4 group and a strip of two edge-sharing octahedra plus an edge sharing PO4 group (Fig. 3b). Furthermore, six PO4 group link the strip by sharing their vertices. The M12O17(OH,F)6½PO4 Š610 unit repeats along [010] by sharing the (OH,F) anions with the adjacent units, forming a column of the form M12O17(OH,F)6½PO4 Š610 . Within the (010) plane, these columns link by sharing (OH,F) anions and vertices of PO4 tetrahedra, plus other (PO4) and (AlO6) groups, as well as the M1 tetrahedron. Monovalent and divalent alkaline-earth cations occur in the interstitial voids as well as within the columns. There are four M12O17(OH,F)6½PO4 Š610 per unit cell. The structure (Fig. 4) shows disorder at alkali sites and P1 sites, which have been modelled as split sites, following Cámara et al. (2006). The refinement converged to a 1/3:2/3 population, not compatible with a missing centre of Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/31/4/823/4840137/ejm_31_4_0823_0836_camara_2868_online.pdf Fluorcarmoite-(BaNa), the first Mg-dominant mineral of the arrojadite group 831 Table 6. The Al and M sites. Main interatomic distances (Å), geometrical parameters and bond valence valuesa (v.u.) for fluorcarmoite(BaNa). Al–O5a –O10a –O5b –O13a –O10b –O13b <Al–O> V(Å3)* M1–O4a –O8b –O12b –O11a –O12a <M1–O> V(Å3) 1.850(6) 1.875(6) 1.884(6) 1.886(5) 1.891(5) 1.892(5) 1.880 8.83 1.843(10) 2.005(6) 2.040(6) 2.051(7) 2.654(7) 2.119 7.35 0.573 0.538 0.525 0.523 0.516 0.515 3.190 M1–O2b 2.862(7) M2a–O4x –O24b –O23a –O19a –O20b <M2a–O> V(Å3) M2b–O23b –O3a –O24a –O20a –O19b <M2b–O> V(Å3) 2.061(5) 2.077(6) 2.079(5) 2.089(6) 2.114(6) 2.084 6.27 2.051(6) 2.068(6) 2.073(6) 2.092(6) 2.097(6) 2.076 6.41 0.388 0.374 0.373 0.364 0.344 1.843 M3a–O14a –O23b –W1 –O19b –O9a –O1a <M3a–O> V(Å3) 2.009(6) 2.020(6) 2.035(6) 2.110(6) 2.111(6) 2.181(6) 2.078 11.73 0.404 0.395 0.291 0.322 0.321 0.274 2.007 0.597 0.414 0.383 0.374 0.096 1.864 0.388 0.373 0.369 0.354 0.350 1.833 M3b–O14b –W2 –O23a –O19a –O9b –O1b <M3b–O> V(Å3) M4a–O1b –O21a –O9b –O7a –O5a –O15a <M4a–O> V(Å3) 1.997(6) 2.024(7) 2.026(6) 2.126(6) 2.127(6) 2.191(6) 2.082 11.83 2.032(6) 2.063(5) 2.111(6) 2.132(6) 2.143(5) 2.212(6) 2.115 12.03 0.425 0.311 0.398 0.318 0.317 0.275 2.044 M4b–O1a –O21b –O9a –O5b –O7b –O15b <M4b–O> V(Å3) M5a–O17b –O2a –O6b –O11b –O14a –O13a <M5a–O> 2.011(6) 2.077(6) 2.078(7) 2.130(5) 2.135(6) 2.236(5) 2.111 11.92 2.025(6) 2.082(6) 2.108(5) 2.110(5) 2.202(6) 2.255(6) 2.130 0.419 0.361 0.360 0.320 0.317 0.252 2.029 M5b–O17a –O6a –O2b –O11a –O14b –O13b <M5b–O> V(Å3) 2.021(5) 2.072(6) 2.089(6) 2.111(6) 2.208(6) 2.275(5) 2.129 12.11 0.422 0.376 0.362 0.345 0.277 0.238 2.021 0.397 0.370 0.332 0.317 0.309 0.265 1.990 0.423 0.372 0.351 0.349 0.284 0.252 2.031 M6a–O18b –O12b –O6a –O2b –O24a –W2 <M6a–O> V(Å3) M6b–O18a –O12a –O6b –O2a –W1 –O24b <M6b–O> V(Å3) 2.024(5) 2.126(6) 2.138(5) 2.249(6) 2.364(7) 2.377(6) 2.213 13.99 2.011(6) 2.120(6) 2.158(6) 2.273(6) 2.284(5) 2.343(6) 2.198 13.74 0.450 0.356 0.346 0.268 0.206 0.142 1.767 M7a–O22a –O7b –O20b –O16a –W1 –O4x <M7a–O> V(Å3) M7b–O22b –O7a –O16b –O20a –W2 –O3a <M7b–O> V(Å3) 2.020(6) 2.056(6) 2.110(6) 2.151(6) 2.194(5) 2.322(5) 2.142 12.62 2.034(6) 2.067(6) 2.113(6) 2.118(6) 2.120(6) 2.491(7) 2.157 12.86 0.420 0.387 0.343 0.312 0.209 0.212 1.884 0.454 0.354 0.324 0.249 0.177 0.212 1.770 0.408 0.378 0.341 0.337 0.256 0.145 1.865 a Bond-valence parameters from Gagné & Hawthorne (2015) for bond with O= and from Brown (1981) for bonds with F . *V = polyhedral volume. symmetry as proposed by other authors (Kallfaß et al., 2010; Vignola et al., 2016). It seems therefore that the apparent presence of a centre of symmetry in some other localities is the result of local disorder due to high-temperature crystal growth. The shape of the electron density at some anion sites is oblate and represents local disorder associated with complex cation order. In particular, disorder is present at Na3 and Na3x, but chemical composition implies that the overall cation occupancy of the Na3 cavity is <0.5 apfu, and thus the third modifier is not required for naming. Consequently, the occupancy of H3x is reduced and explains – along with the fluorine content – the weak bands observed in the OH-stretching region of the Raman spectrum. Using the chemical analysis and the observed site scattering, it is also possible to assign ions to specific sites (Table 8). The agreement is very good. The incident bond-valence in Table 4 validates the model. Anions at the W1 and W2 sites show incident bond-valence <1 valence units (v.u.) characteristic of F ions or (OH) groups. The other anion sites are O3b0 and O3bx, which are two split sites related to the disorder of the P1 sites and to the partial occupancy of the Na3 site by Na and K (or H in case of vacancy at the Na3 site). In Table 8, the ordering of Fe2+ (and Mn2+) is evident, with preference for the distorted M2a, M5a,b as well as the more regular but still larger M6a,b sites. In particular, some Na is disordered over the M6a,b and M7a,b sites, in agreement with the site scattering as well as mean bondlength. Na can therefore disorder the inter-column sites and the octahedra, exchanging with Fe2+. This exchange is probably related to high-temperature crystallization, in Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/31/4/823/4840137/ejm_31_4_0823_0836_camara_2868_online.pdf 832 F. Cámara et al. Table 7. The alkali sites. Selected interatomic distances (Å), geometrical parameters and bond valence valuesa (v.u.) for fluorcarmoite(BaNa). A1–O18b –O18a –O22a –O22b –O17b –O17a –O21a –O21b <A1–O> V(Å3)* B1–O8a –O11b –O12a –O2a –O15b <B1–O> V(Å3) 2.749 (6) 2.758 (6) 2.770 (6) 2.798 (6) 2.863 (6) 2.887 (6) 2.898 (5) 2.919 (6) 2.830 31.59 2.154 (7) 2.335 (7) 2.426 (7) 2.528 (7) 3.144 (7) 2.517 12.68 0.264 0.258 0.251 0.234 0.200 0.188 0.183 0.174 1.754 B1–O3b0 1.170 (7) B1b–O3b0 –O12a –O11b –O8a –O12b <B1b–O> V(Å3) 2.014 (6) 2.045 (6) 2.057 (6) 2.078 (7) 2.533 (6) 2.146 7.74 0.149 0.139 0.135 0.129 0.047 0.598 B2–O13a –O10a –O24b –O20b –O21b –O17b –O16a –O5b <B2–O> V(Å3) 2.313 (7) 2.352 (7) 2.388 (7) 2.398 (7) 2.473 (7) 2.599 (8) 2.703 (7) 3.081 (7) 2.538 24.95 0.179 0.163 0.150 0.146 0.122 0.091 0.071 0.029 0.951 0.137 0.089 0.072 0.056 0.013 0.368 B2b–O10a –O16a –O24b –O20b –O13a –O3b0 –O4x –O21b <B2b–O> V(Å3) Caa–O16b –O8b –O15a –O4a –O8a –O16a –O7a –O15b <Caa–O> V(Å3) Cab–O8a –O16a –O15b –O3b0 –O8b –O16b –O15a –O7b <Cab–O> V(Å3) Na1–O14a –O14b –O15a –O15b –O9a –O9b –O11b –O11a <Na1–O> V(Å3) 2.278 (12) 2.352 (12) 2.363 (12) 2.476 (12) 2.543 (13) 2.815 (15) 2.948 (13) 3.049 (14) 2.603 26.78 2.210 (7) 2.223 (7) 2.274 (7) 2.296 (9) 2.430 (8) 2.590 (7) 2.793 (7) 2.917 (8) 2.467 25.28 2.160 (8) 2.225 (7) 2.327 (8) 2.369 (8) 2.452 (7) 2.526 (7) 2.829 (8) 2.913 (7) 2.475 25.32 2.342 (8) 2.385 (7) 2.473 (8) 2.487 (8) 2.611 (8) 2.638 (8) 2.686 (9) 2.738 (9) 2.545 25.09 0.055 0.046 0.045 0.034 0.029 0.015 0.011 0.009 0.244 0.215 0.208 0.183 0.174 0.125 0.085 0.052 0.038 1.079 0.264 0.225 0.175 0.158 0.129 0.108 0.051 0.042 1.153 0.210 0.190 0.154 0.149 0.111 0.104 0.093 0.082 1.091 Na2–O10b –O13b –O24a –O20a –O21a –O16b –O17a –O5a <Na2–O> V(Å3) Na3–O3a –O1b –O4x –O1a –O23a –O23b –O19b –O19a <Na3–O> V(Å3) Na3x–O3a –O19b –O1b –O19a –O2b –O4x –O1a <Na3x–O> V(Å3) 2.296 (6) 2.317 (7) 2.362 (7) 2.428 (7) 2.591 (8) 2.663 (8) 2.676 (8) 3.152 (8) 2.561 25.22 2.45 (6) 2.74 (5) 2.76 (6) 2.86 (5) 3.07 (6) 3.10 (6) 3.17 (5) 3.19 (5) 2.92 29.41 2.495 (13) 2.735 (15) 2.760 (13) 2.821 (15) 2.827 (13) 3.138 (13) 3.148 (13) 2.846 23.61 Na3x–O3bx Na3–O3bx 0.939(14) 1.19 (4) 0.203 0.193 0.174 0.148 0.101 0.085 0.082 0.026 1.013 0.054 0.026 0.025 0.019 0.011 0.011 0.009 0.008 0.165 0.033 0.018 0.017 0.015 0.015 0.007 0.007 0.113 a Bond-valence parameters from Gagné & Hawthorne (2015) for bond with O= and from Brown (1981) for bonds with F . *V = polyhedral volume; bond valence in split sites (B1 and B1b, B2 and B2b, Caa and Cab, Na3 and Na3x) correspond to the partial occupancies at these sites. agreement with the split model for P1 and some alkali sites. Note that the observed site distribution of Mg and Fe2+(Mn2+) in fluorocarmoite-(NaBa) (Table 8) agrees closely with the site populations of Cámara et al. (2006) in samples from Rapid Creek and Horrsjöberg, which have lower Mg (2.69 and 3.61 apfu, respectively). 8. Related minerals Fluorcarmoite-(BaNa), A1BaA2hB1,2NaNa1,2Na2Na3hhCaCa (Mg,Fe2+,Mn2+)12Al(PO4)11(PO3OH)F2, is a new member of the arrojadite group (Table 9). Provided that the environment is low in Fe and Mn, it seems possible to find other members of the arrojadite group with the root-name carmoite. The other sample reported in literature with high, but not dominant Mg-content is sample Gentile-154 from Spluga Valley (Lombardy, Italy; Demartin et al., 1996; Chopin et al., 2006), which has up to 5.68 Mg apfu (lower than the 8.12 apfu of Fe2+, the dominant element). The refinement of Demartin et al. (1996) shows Mg ordered preferentially at the M1, M3 and M4 sites, in agreement with the findings of this study for the Mg-dominant end-member. Nowadays, the structure of phosphates containing large channels is of interest in Material Sciences because of the possibility to use their analogues as feasible novel alkalimetal ion batteries (Trad et al., 2010). In particular, sulphate analogues of alluaudite have been tested and show promising properties (Marinova et al., 2015). Preliminary tests on materials with the arrojadite topology have been done by Kallfaß et al. (2011), who described it as a novel cathode material which exhibits an excellent cycle behaviour Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/31/4/823/4840137/ejm_31_4_0823_0836_camara_2868_online.pdf by UNIVERSITA DEGLI STUDI DI MILANO user Fluorcarmoite-(BaNa), the first Mg-dominant mineral of the arrojadite group 833 Table 8. Site-scattering values* and site occupancies (excluding P sites). Site Occupancy A1 A2 Bl B2 Na1 Na2 Na3 Ca (Ba0.93Sr0.05)R0.98 (h) (Na0.41Fe2þ 0:33 )R0.74 Na0.98 Na0.98 Na0.85 (Na0.22K0.15)R0.37 Ca0.94 Al M1 M2a M2b M3a M3b M4a M4b M5a M5b M6a M6b M7a M7b (Al0.97Fe3þ 0:02 h0.01)R1 (Mg0.88Fe2þ 0:12 )R1 (Mg0.39Fe2þ 0:61 )R1 (Mg0.58Fe2þ 0:42 )R1 Mg1 (Mg0.82Fe2þ 0:18 )R1 (Mg0.75Fe2þ 0:24 Mn0.01)R1 (Mg0.70Fe2þ 0:29 Mn0.01)R1 (Mg0.37Fe2þ 0:61 Mn0.02)R1 (Mg0.46Fe2þ 0:52 Mn0.02)R1 (Mg0.18Fe2þ 0:74 Mn0.25Na0.10)R1 (Mg0.29Fe2þ 0:40 Mn0.19Na0.12)R1 (Mg0.55Fe2þ 0:37 Mn0.03Na0.05)R1 (Mg0.55Fe2þ 0:35 Mn0.04Na0.06)R1 eps (calc) 54 eps (obs) 54.0(8) 13.1 10.8 10.8 9.4 5.3 18.8 R 122.2 13.1 13.7 20.5 18.3 12 14.5 15.5 16.2 20.8 19.5 21.7 20 17.5 17.4 R 240.3 11.67(6) 11.0(1) 10.6(1) 9.90(1) 7.5(1.4) 20.0(1) R 124.7 12.7(2) 13.4(1) 20.2(1) 17.5(1) 11.4(2) 14.1(1) 15.0(1) 15.8(1) 20.3(1) 19.2(1) 21.3(1) 19.6(1) 17.1(1) 17.0(1) R 234.6 R 362.5 R 359.3 *In the sense of Hawthorne et al. (1995), in electrons per site (eps). Fig. 3. The M12O17(OH,F)6½PO4 Š610 unit from [010] (a) and onto (100) (b), with details of the two building strips. M sites in orange, P sites in violet. Drawing obtained with VESTA 3 (Momma & Izumi, 2011). Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/31/4/823/4840137/ejm_31_4_0823_0836_camara_2868_online.pdf 834 F. Cámara et al. Table 9. Arrojadite group. Comparison of three different root-name members of the group. Fluorcarmoite-(BaNa) Arrojadite-(KNa) Dickinsonite-(KMnNa) Reference Ideal formula (1) (2) (2) KNa3(CaNa2)Fe2þ K(NaMn)CaNa3AlMn13 BaNaCaNa2Mg12Al(PO4)11 13 Al(PO4)11 (PO3OH)F2 (PO3OH)(OH)2 (PO4)12(OH)2 Crystal system Monoclinic Monoclinic Monoclinic Space group Cc Cc Cc a (Å) 16.4013(3) 16.5220(11) 16.6900(9) b (Å) 9.9487(1) 10.0529(7) 10.1013(5) c (Å) 24.4536(8) 24.6477(16) 24.8752(13) b (°) 105.725(2) 106.509(2) 105.616(2) V (Å3) 3840.80(15) 3932.2(7) 4038.9(7) Z 4 4 4 Axial ratios (a:b:c) 1.649:1:2.458 1.643:1:2.452 1.652:1:2.463 3.40 Unknown Unknown Dmeas (g cm 3) Dcalc (g cm 3) 3.394 3.437 3.496 3.04(100), 2.717(80), 3.049(100), 2.691(71), Strongest lines in 3.012(100), 2.682(39), 3.22(60), 2.85(45), 5.861(29), 2.793(28), 5.026(28), powder pattern: dobs (Å)(I) 2.735(32), 2.818(28), 5.93(40), 2.770(40), 2.554(35) 2.798(25), 2.777(24) 3.188(28), 2.526(25), 4.959(25), 4.570(24), 4.150(22), 4.5242(20) Optical character Biaxial (+), na = 1.6240(5), Biaxial (+), na = 1.651(1), Biaxial (+), na = 1.658, nb = 1.6255(5), nb = 1.656(1), nb = 1.662, nc = 1.671 (589 nm), nc = 1.6384(5) (589 nm), nc = 1.662(10) (589 nm), 2Vcalc. = 68° 2Vmeas. = 35(2)°, 2Vcalc. = 38° 2Vmeas. = 87.8(1)°, 2Vcalc. = 85° Colour Yellow–orange Yellow Vivid Green Hardness 7 5 3.5–4 Streak Yellow–orange White White Luster Vitreous Vitreous Vitreous Habit and forms Anhedral crystals Euhedral platy prismatic Mica-like platelets Rapid Creek, Dawson mining district, Fillow Quarry, Branchville, Type locality “Costa Balzi Rossi”, Yukon Territory, Canada Ridgefield, Fairfield County, Maremola Creek, Isallo, Connecticut, USA Magliolo, Savona, Liguria, Italy Associations Quartz, (fluorapatite, and possible Euhedral quartz and some Eosphorite, triploidite, graftonite inclusion) “limonite” (former siderite?) lithiophilite, quartz References: (1) This study; (2) Cámara et al. (2006). Fig. 4. The four M12O17(OH,F)6½PO4 Š610 units per unit cell. P3a,b and M1 tetrahedra, Al octahedra as well as alkaline site atoms have been removed for the sake of simplicity. Colours as in Fig. 3. Drawing obtained with VESTA 3 (Momma & Izumi, 2011). Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/31/4/823/4840137/ejm_31_4_0823_0836_camara_2868_online.pdf Fluorcarmoite-(BaNa), the first Mg-dominant mineral of the arrojadite group because lithium content has little effect on its structure stability. The high variability of cation coordination and radius in the arrojadite structure makes it a promising candidate, particularly the Mn-endmember fluordickinsonite(NaNaNa). Acknowledgements: FC thanks Christian Chopin for involving him in the study of arrojadites, one of the most complex structures FC has dealt with. The paper benefited from the journal reviews made by Frank C. Hawthorne and an anonymous reviewer, and Guest Editor W. Maresch. 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