Pautovite, CsFe2S3, a new mineral species from the Lovozero alkaline complex, Kola Peninsula, Russia

Pautovite, the cesium-dominant analogue of rasvumite and picotpaulite, is a new mineral species found in the Palitra peralkaline pegmatite, Kedykverpakhk Mountain, Lovozero alkaline complex, Kola Peninsula, Russia. It is associated with belovite-(Ce), villiaumite, aegirine, ussingite, natrosilite, microcline, sodalite, potassicarfvedsonite, serandite, nordite-(Ce), ferronordite-(Ce), bornemanite, vuonnemite, lomonosovite, vitusite-(Ce), phosinaite-(Ce), barytolamprophyllite, mangan-neptunite, manaksite, chkalovite, kapustinite, kazakovite, steenstrupine-(Ce), thorosteenstrupine, bario-olgite, nalipoite, sphalerite, lollingite, wurtzite, bartonite, chlorbartonite, and zakharovite, among others. Pautovite occurs in a hydrothermal assemblage as crudely prismatic to acicular crystals up to 120 mu m long and up to 15 mu m thick, typically forming subparallel overgrowths on belovite-(Ce). Twinning was not observed. Pautovite is opaque, dark steel-grey with a strong metallic luster, becoming dull black on exposure to moist air. It is flexible. Cleavage is perfect on {110}, and the fracture is splintery. D(calc.) equals 3.85(l) g/cm(3). The density and hardness could not be measured, and the streak could not be observed because of the minute size of the crystals. In reflected light, pautovite is strongly bireflectant, with distinct pleochroism from greyish white to grey with a slight pinkish tint. The anisotropy is strong in pale brownish tints. No internal reflections were observed. Reflectance values (lambda in nm: R-1, R-2, in %); measured in air (SiC standard) are: 470: 14.0, 24.6; 546: 14.7, 23.5; 589: 15.2, 24.6; 650: 16.0, 27.1; values are presented for the interval 400-700 nm. A chemical analysis by electron microprobe gave: K 0.21, Rb 1.31, Cs 36.12, Tl 0.50, Fe 33.80, S 28.85, total 100.79 wt.%. The empirical formula, based on a sum of six atoms, is (Cs0.91Rb0.05K0.02Tl0.01)Sigma 0.99Fe2.02S2.99. The idealized formula is CsFe2S3, which requires: Cs 39.00, Fe 32.78, S 28.22 wt.%. Pautovite is orthorhombic, Cmcm (by analogy with other representatives of the rasvumite structure-type, including synthetic CsFe2S3)-Unit-cell dimensions: a 9.477(4), b 11.245(4), c 5.485(2) angstrom, V 584.5(6) angstrom(3), Z = 4. The strongest lines of the X-ray powder diagram [d in angstrom (I)(hkl)] are: 4.69(30)(200), 4.28(20)(111), 2.981(100)(221), 2.723(40)(002), 2.003(30)(312,151,421), 1.910(60)(042, 060), 1.785(30)(402), and 1.565(40)(313). The name honors Leonid A. Pautov (b. 1958), in recognition of his studies of minerals by physical methods. Both the mineral and its name have been approved by the IMA Commission on New Minerals and Mineral Names (IMA no. 2004-005).