ZAVALIAITE, (Mn2+,Fe2+,Mg)3(PO4)2, A NEW MEMBER OF THE SARCOPSIDE GROUP FROM THE LA EMPLEADA PEGMATITE, SAN LUIS PROVINCE, ARGENTINA

Zavaliaite, (Mn2+,Fe2+,Mg)(3)(PO4)(2), belongs to the sarcopside group of minerals and corresponds to the Mn2+ equivalent of sarcopside and chopinite. It occurs at the La Empleada pegmatite, San Luis Province, Argentina. Zavaliaite forms colorless and transparent exsolution-lamellae up to 70 mu m thick and 1.5 mm long in lithiophilite. Owing to hydration, the mineral partially hydrates to reddingite, (Mn2+,Fe2+)(3)(PO4)(2)center dot 3H(2)O. Lamellae of zavaliaite display a perfect cleavage along the {100} or {001} direction. The luster is vitreous to resinous, and the streak is white. Optically, the mineral is biaxial (-), with an average index of refraction of 1.66(1) (for lambda = 589 nm), 2V(meas) = 15(5)degrees. It is non-pleochroic, without dispersion; the cleavage plane shows an angle of ca. 45 degrees with the elongation of the lamellae; X is perpendicular to this cleavage plane. Zavaliaite is non-fluorescent under short-wave and long-wave ultraviolet light, and its calculated density is 3.68 g/cm(3). The mineral is brittle, with a Mohs hardness of 4. The mean chemical composition, determined with an electron microprobe from 27 point analyses (wt.%), is: P2O5 41.38, FeO 24.94, MgO 6.09, MnO 27.08, total 99.49. The empirical formula, calculated on the basis of eight atoms of oxygen per formula unit, is (Mn1.312+Fe1.192+Mg0.52)(Sigma 3.02)(P1.00O4)(2). Zavaliaite is monoclinic, space group P2(1)/c, a 6.088(1), b 4.814(1), c 10.484(2)angstrom, beta 89.42(3)degrees, V 307.2(1) angstrom(3), and Z = 2. The crystal structure is identical to that of sarcopside and chopinite, with the M1 site occupied by 0.5 Fe2+ + 0.35Mn(2+) + 0.15 Mg, and the M2 site occupied by 0.475 Mn2+ + 0.35 Fe2+ + 0.175 Mg. The strongest eight lines in the X-ray powder pattern [d in angstrom (intensities estimated visually) (hkl)] are: 6.75 (very strong) (100), 3.54 (weak) (012)(11 (1) over bar), 2.964 (strong) (200), 2.816 (weak) (013), 2.537 (strong) (11 (3) over bar), 1.894 (very strong) (220), 1.848 (very strong) (311), and 1.652 (very strong) (31 (3) over bar)(313). The mineral has been approved by the Commission on New Minerals and Mineral Names of the International Mineralogical Association [IMA 2011-012], and is named in honor of Maria Florencia de Fatima Marquez Zavalia [or Marquez-Zavalia], investigator of Argentinian minerals and ore assemblages and Head of the Department of Mineralogy, Petrography and Geochemistry, IANIGLA, CCT Mendoza, CONICET (National Research Council of Argentina).