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macla nº 13. septiembre ‘10 revista de la sociedad española de mineralogía 97

Fontarnauite, a New Sulphate-Borate from the Emet Borate District

(Turkey) / JAVIER GARCÍA-VEIGAS (1,*), LAURA ROSELL (2), XAVIER ALCOBÉ (1), IGNACIO SUBIAS (3), FEDERICO ORTÍ (2), İBRAHIM GÜNDOĞAN (4), CAHIT HELVACI (4) (1) Serveis Cientificotècnics, Universitat de Barcelona (SCT-UB). 08028, Barcelona (España) (2) Departament de Geoquímica, Petrologia i Prospecció Geològica, Universitat de Barcelona. 08028, Barcelona (España) (3) Departamento de Ciencias de la Tierra, Universidad de Zaragoza. 50009, Zaragoza (España) (4) Dokuz Eylül Üniversitesi, Jeoloji Mühendisliği Bölümü, Tinaztepe Kampüsü. 35160, Buca-Ízmir (Turkey)

INTRODUCTION. alternation of Na-Ca borate (probertite) Other minor found in the and Na-Ca sulphate () units boreholes include: borates (aristarainite, Fontarnauite is a new mineral found in including a central deposit. , , kaliborite core samples belonging to Doğanlar Colemanite is restricted to the base and tunellite and ulexite), sulphates boreholes nº2 and nº188 drilled in the top of the sequence. (anhydrite, celestine, , vicinity of the Doğanlar village, located kalistrontite and thenardite), and four kilometres to the southwest of the sulphides (arsenopyrite, orpiment and Emet town (Western Anatolia, Turkey). realgar).

Fontarnauite is a double salt (borate- PHYSICAL AND OPTICAL PROPERTIES. sulphate) of sodium and strontium with minor contents of potassium and Fontarnauite occurs as colourless or calcium. So far no borates of a Sr- and slightly brown isolated crystals, or as Na-containing sulphate group have been crystal clusters (Fig. 1), with prismatic reported before. Despite the mm-size, sections less than 5 mm long. More single crystals have been impossible to often it displays pseudohexagonal obtain, thus hindering the appropriate sections less than 1 mm in diameter. characterization required for the Under electron microscope it shows a recognition as a new mineral by the perfect parallel to (010) (Fig. CNMNC-IMA. 2). It has a pearly, transparent to translucent , a brittle tenacity and The proposed name is for deceased Dr. a white . Ramon Fontarnau (1944-2007), Director of the Material Characterization Section the Scientific-Technical Survey oat the University of Barcelona. It seems a fitting and deserving honour, given his effort to promote the development of scientific facilities focused on, among fig 1. Optical (upper) and BSE-SEM (lower) images of a cluster of fontarnauite crystals. (F: fontarnauite, P: others, mineral characterization. probertite, T: tuff).

GEOLOGICAL SETTING. Sedimentary and early diagenetic processes controlled the crystal growth The western Anatolia borate deposits both subaqueously and interstitially. (Turkey) consist of five separated Moreover bacterially inducing dolomite districs: Bigadiç, Sultançayir, Kestelet, precipitation occurred. The composition Emet and Kirka, all of them formed of fluid inclusions in halite samples fig 2. BSE-SEM image of fontarnauite showing a perfect cleavage and replacing a fine-grained during the Miocene in closed lacustrine indicates high K concentrations in SO4- basins during periods of high probertite. rich brines. Kalistrontite is abundant in volcanic and hydrothermal activity. the sequence indicating a significant Although the mineral association of Optically, it is biaxial negative and non- concentration of Sr in brines. pleochroic. It is colourless and displays borates varies in each district, they are Fontarnauite appears as an early generally interbedded with series of low positive relief in thin section. diagenetic phase, replacing both Interference colours in prismatic tuffaceous deposits. The principal borate probertite and glauberite, as a mineral outcropping in several open pit sections are first-order grey and white consequence of a particular K-SO4 (Fig. 3). Centred acute bisectrix figures mines in the Emet basin is colemanite composition achieved by the residual with minor amounts of ulexite and with numerous isochromes are obtained brines during evaporation in a saline on sections parallel to (010). Optic axis hydroboracite (Helvacı and Ortí, 1998). lake environment with volcaniclastic The mineralogical record of Doğanlar dispersion is medium to weak (r > v) and contribution. crossed bisectrix dispersion is distinct. boreholes is characterized by the

palabras clave: boratos, evaporitas, Mioceno. key words: borates, , Miocene.

resumen SEM 2010 * corresponding author: [email protected]

98

Optical orientation is X = b, OAP ┴ (010). expected at 540-590 cm-1 is missing reported after Le Bail fitting. Main X-ray

(Jun et al. 1995) suggesting the powder diffraction data (in Å for CuKα1) elimination of one water molecule from are given in Table 2. the poliborate anion to give the one- dimensional chain of composition ACKNOWLEDGEMENTS. 2 [B4O6(OH)2] . This study was supported by projects According to stoichiometry and CGL 2009-1106 and 2009 SGR 1451 of

molecular spectroscopy, and pending the Spanish and Catalan Governments the determination of the crystal respectively. The authors are indebted to structure, fontarnauite could be the staff of the SCT-UB for the technical classified as tetraborate with a proposed assistance, to Jordi Illa (UB) who

ideal formula: prepared the thin sections and to fig 3. Prismatic fontarnauite crystals in thin section (Na,K)2(Sr,Ca)SO4[B4O6(OH)2]·3H2O. Natalie Nahill (University of with crossed polars. Considering the Sr and Na Pennsylvania) for English revision.

predominance, the hypothetical end- CHEMICAL COMPOSITION. member formula should be (I/I0)1000 d (Å) h k l Na2SrSO4[B4O6(OH)2]·3H2O which 1000 11.1498 0 2 0 Chemical analysis (Table 1) has been requires Na2O: 13.56, SrO: 22,68, SO3: 199 3.3389 0 4 2 obtained by Electron Microprobe using a 17,52, B2O3: 30.47 and H2O + OH: Mo/B4C-layered synthetic crystal (McGee 15.76. 100 3.0458 0 5 2 et al. 1991). Moderate energy (15 kV), 78 3.3948 0 6 1 low intensity current (6 nA), large beam wt % range 75 2.3999 2 6 0 diameter (10 μm) and a short counting B2O3 30.22 29.72 - 31.94 time (10 s) were applied to avoid 71 3.0250 2 2 0 mobilization of and sodium. Na2O 16.65 12.23 – 13.24 71 2.2300 0 10 0 SO3 17.77 17.00 – 18.60 Accuracy > 95% for boron analysis in 66 3.1990 -1 4 2 fontarnauite was obtained analyzing the K2O 1.69 0.87 – 2.20 contents in probertite and kaliborite 65 7.8104 0 1 1 CaO 2.25 1.41 – 3.69 64 6.2859 1 0 0 crystals present in the same samples. Water content (including OH) was SrO 19.01 16.58 – 20.81 62 3.9061 -1 0 2 estimated by difference. Divalent H2O* 16.41 58 2.9760 0 7 1 cations (Sr and Ca) show significant variations (Fig. 4) According to chemical Total 100.00 55 3.1429 2 0 0 Table 2. Principal intensities of X-ray powder data Table 1. Analitycal data (EPMA) for fontarnauite. data, the empirical formula (based on for fontarnauite. 15 O atoms) is: (*water content, including hydroxyl, by difference).

(Na1.84K0.16)Σ2(Sr0.83Ca0.18)Σ1.01B3.91S1.01H CRYSTALLOGRAPHY. REFERENCES. 8.21O15, or (NaK)2(SrCa)B4SH8O15.

Helvacı, C. & Ortí, F. (1998): Sedimentology Single-crystal study could not be carried and diagenesis of the Miocene colemanite- out because of the unavailability of ulexite deposits (Western Anatolia, Turkey). suitable crystals. Although the powder J. Sed. Research, 69, 1021-1033. diffraction analysis shows the presence Jun, L., Shuping, X., Shiyang, G. (1995): FT-IR of probertite as a minor phase, most of and Raman spectroscopic study of the peaks observed in the diagram do hydrated borates. Spectrochimica Acta, 51, not match any reported phase. 519-532. Le Bail, A., Duroy, H., Fourquet, J.L. (1988): Ab initio structure determination of LiSbWO6 Indexation using DICVOL04 (Loüer and by X-ray powder diffraction. Materials Boultif, 2006) took into account all Research Bulletin, 23, 447-452. fig 4. Sr versus Ca contents. observed peaks except those assigned Loüer, D. & Boultif, A. (2006): Indexing with to probertite. A monoclinic cell was sccesive diochotomy method, DICVOL04- FTIR spectrum at environmental found and the space group P21/c Zeitschrift für Kristallographie conditions shows a broad band with four determined from the systematic Supplements, 23, 447-452. overlapping peaks between 3587 and absences. To check the cell parameters McGee, J.J., Slack, J.F., Herrington, C.R. -1 3208 cm assigned to OH stretching and space group, a profile pattern (1991): Boron analysis by electron microprobe using MoB4C layered synthetic frequencies. B-O frequencies are matching fitting procedure was carried consistent with the presence of the crystals. Am. Mineralogist, 76, 681-684. out using the Le Bail method (Le Bail et Rodríguez-Carvajal, J. (1990): FullProf: A hydrated tetraborate [B4O5(OH)4]2- al., 1988) and by means of the FullProf program for Rietveld refinement and containing both trigonal planar (BO3) and program (Rodríguez-Carvajal, 1990). The pattern matching analysis. Abstracts of the tetrahedral (BO4) fragments (Jun et al., calculated powder X-ray diffraction Satellite Meeting on Powder Difracction of 1995). A Raman spectrum (Fig. 4) diagram of probertite was considered in the XV Congress of the IUCr, p. 127. shows the fundamental symmetric the fitting procedure. The reported cell Toulouse. stretching vibration of the sulphate parameters (a: 8.456, b: 22.3004, c: group. As occurs in the 8.5615, β: 103.095 ź, and V: 1200.11 symmetric vibration of tetraborate anion Å3, Z: 4, density: 2.39 g/cm3) has been