Abstract:

Ferro-pedrizite, a new amphibole-supergroup mineral was discovered in the Sutlug pegmatite occurrence situated in the Targi River Basin, Tyva Republic, Eastern Sibera, Russia. The associated minerals are quartz, albite, microcline, spodumene, cassiterite, beryl, columbite-(Mn), fergusonite-β-(Y), fluorapatite, schorl, trilithionite and fluorite. Ferro-pedrizite forms dark grey-blue to violet-blue acicular and long prismatic crystals up to 2 × 5 × 50 mm and their aggregates. Dmeas = 3.16(1) g/cm3 (by hydrostatic weighing), 3.13(1) g/cm3 (by flotation in heavy liquids); Dcalc = 3.135 g/cm3. Ferro-pedrizite is optically biaxial (−), α = 1.614(3), β = 1.638(3), γ = 1.653(3), 2Vmeas = 75(5), 2Vcalc = 76. The infrared spectrum is given. The chemical composition is (EDS-mode electron microprobe, the ratio Fe2+:Fe3+ by Mössbauer data, Li by ICP-MS, H2O by gas chromatography of ignition products, F by wet analysis, wt. %): Li2O 4.67, Na2O 2.54, K2O 0.13, MgO 4.48, CaO 0.29, MnO 0.59, FeO 9.06, Al2O3 13.13, Fe2O3 4.60, SiO2 57.59, F 1.15, H2O 1.50, -O = F–0.48, total 99.25. The empirical formula based on 24 anions is: (Na0.60K0.02)∑0.62(Li1.89Na0.07Ca0.04)∑2.00(Fe2+1.03Mg0.90Mn2+0.07Al1.88Fe3+0.47Li0.65)∑5.00[(Si7.79Al0.21)∑8.00O22][(OH)1.36F0.49O0.15)]. The simplified formula is NaLi2(Fe2+2Al2Li)Si8O22(OH)2. Ferro-pedrizite is monoclinic, C2/m, a = 9.3716(4), b = 17.649(1), c = 5.2800(6) Å, β = 102.22(1), V = 853.5(1) Å3, Z = 2. The structure has been refined to Robs = 3.9 % (4843 I > 2σI). A twinning model was introduced into the refinement through the matrix [−1 0 0/0−1 0/−0.7516 0 1] with the ratio of two twin components of 0.681(3)/0.319(3). The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 8.147 (52) (110), 4.420 (22), (040), 3.009 (100) (310), 2.7102 (28) (330), 2.6865 (29) (151), 2.6236 (21) (461). Type material is deposited in the Mineralogical Museum of the Tomsk State University, Tomsk, Russia.

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