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

GALLISKI, M. A. ČERNÝ, P., MÁRQUEZ ZAVALÍA, MARÍA FLORENCIA Y CHAPMAN, R.,

AMERICAN MINERALOGIST

Allen Press Inc.

Lugar: Kansas; Año: 1999 vol. 84 p. 773 - 777

0003-004X

Ferrotitanowodginite is a new mineral of the wodginite group, which is found in and defined fromtwo closely adjacent pegmatites in the San Luis province, Argentina, but previously encountered in the Tanco (Manitoba) and Marko’s (Ontario) pegmatites. In the San Elías pegmatite,ferrotitanowodginite occurs aggregated with ferrowodginite and associated with microlite,ferrotapiolite, cleavelandite, and quartz. In La Viquita pegmatite, ferrotitanowodginite occurs in areplacement unit associated with wodginite, ferrowodginite, titanowodginite and ferrotapiolite inyellow muscovite and quartz. Ferrotitanowodginite is very dark brown to black, with a dark brownstreak and submetallic luster. Mohs hardness is 51/2 and Dcalc = 7.368 g/cm3. In reflected light, it is creamy white and gray in air and oil, respectively; anisotropy is distinct, bireflectance and pleochroism moderate. Ferrotitanowodginite is monoclinic, space group C2/c, Z = 4. Unit-cell dimensions for San Elías’material are a = 9.403(4) Å, b = 11.384(3) Å, c = 5.075(1) Å, b = 90.55° (2), V = 543.24(22) Å3. The strongest lines in the X-ray powder diffraction are d = 2.963 Å, I = 100%, (hkl = 221 – ); d = 2.939 Å, I = 90% (hkl = 221); d = 3.626 Å, I = 70% (hkl = 220); and d = 1.715 Å, I = 50% (hkl = 402).Eighteen analyses by electron microprobe gave the following mean composition: 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 is much richer in Mn and Sn. The simplified formula for ferrotitanowodginite is: (Fe2+,Mn2+)(Ti,Sn4+,Ta,Fe3+) (Ta,Nb)2O8, ideally Fe2+TiTa2O8.