Ferrotitanowodginite, Fe2+TiTa2O8, a new mineral of the wodginite group from the San Elias pegmatite, San Luis, Argentina

Ferrotitanowodginite is a new mineral of the wodginite group, which is foun d in acid defined from two closely adjacent pegmatites in the San Luis prov ince, Argentina, but previously encountered in the Tanco (Manitoba) and Mar ko's (Ontario) pegmatires. In the San Elias pegmatite, ferrotitanowodginite occurs aggregated with ferrowodginite and associated with microlite, ferro tapiolite, cleavelandite, and quartz. In La Viquita pegmatite, ferrotitanow odginite occurs in a replacement unit associated with wodginite, ferrowodgi nite, titanowodginite and ferrotapiolite in yellow muscovite and quartz. Fe rrotitanowodginite is very dark brown to black, with a dark brown streak an d submetallic luster. Mohs hardness is 5 1/2 and D-calc = 7.368 g/cm(3). In reflected light, it is creamy white and gray in air and oil, respectively; anisotropy is distinct, bireflectance and pleochroism moderate. Ferrotitan owodginite is monoclinic, space group C2/c, Z = 4. Unit-cell dimensions for San Elias' material are a = 9.403(4) Angstrom, b = 11.384(3) Angstrom, c = 5.075(1) Angstrom, beta = 90.550 (2), V = 543.24(22) Angstrom(3). The stro ngest lines in the X-ray powder diffraction are d = 2.953 Angstrom, I = 100 %, (hkl = 22 (1) over bar); d = 2.939 Angstrom, I = 90% (hkl = 221); d = 3. 626 Angstrom, I = 70% (hkl = 220); and d = 1.715 Angstrom, I = 50% (hkl = 4 02). Eighteen analyses by electron microprobe gave the following mean compo sition: WO3 0.02, Nb2O5 6.52, Ta2O5 70.68, TiO2 7.10, SnO2 1.25, ThO2 0.01, UO2 0.02, As2O3 0.03, Sb2O3 0.02, Bi2O3 0.03, Fe2O3 2.18, MgO 0.01, CaO 0. 01, MnO 1.05, FeO 10.27, PbO 0.05, total 99.25 wt%. The La Viquita sample i s much richer in Mn and Sn. The simplified formula for ferrotitanowodginite is: (Fe2+, Mn2+) (Ti,Sn4+,Ta,Fe3+) (Ta,Nb)(2)O-8, ideally Fe2+TiTa2O8.