FERROTOCHILINITE, 6FeS·5Fe(OH)<sub>2</sub>, A NEW MINERAL FROM OKTYABR'SKOYE ORE DEPOSIT (NORILSK ORE DISTRICT, SIBERIA, RUSSIA)
A new mineral ferrotochilinite, 6FeS · 5Fe(OH)2 ideally, has been found at the Oktyabr'skoye copper- nickel deposit in Norilsk ore district, Krasnoyarsky Krai, Russia. In association with ferrotochilinite, magnetite and Fe-rich chlorite-like phyllosilicate it occurs in cavities of the pentlandite-mooihoekite- cubanite ore with subordinate magnetite and chalcopyrite. Ferrotochilinite forms there flattened on [001], prismatic to elongated lamellar crystals up to 0.1 x 05 x 3.2 mm in size, typically split and curved. Its aggregates (up to 6.5 mm in size) are fan-like, rosette-like or chaotic ones. Ferrotochilinite is dark bronze-colored. Its streak is black, luster - moderately metallic. The Mohs' hardness ≈ 1; VHN is 13 kg/mm2. Cleavage is {001} perfect, mica-like. Individuals are flexible, inelastic. D(calc) = 3.467 g/cm3. In reflected light, ferrotochilinite is gray, with hue changing from pale beige to bluish, with distinct bireflectance. Anisotropy is distinct, with gray-bluish to yellowish-beige rotation of colors. No internal reflections. Reflectance values [R1-R2, % (λ, nm)] are 11.6-11.4 (470), 11.2-12.4 (546), 11.1-13.6 (589), 11.0-15.5 (650). IR spectrum shows the presence of (OH) groups bonded with Fe cations and the absence of H2O molecules. Chemical composition (wt %; electron probe, the H content calculated) is: Mg 0.02, Fe 61.92, Ni 0.03, Cu 0.09, S 19.45, O 16.3, Hcalk 103, total 98.84. The empirical formula calculated on the basis of 6 S atoms is: Mg0.01Fe10.96Ni0.005Cu0.015S6(OH)10.07=(Fe5.98Cu0.015Ni0.005)Σ6S6 · (Fe2+4.89 Mg0.01 )Σ4.90(OH)9.80 · F3+0.09(OH)0.27. Ferrotochilinite is monoclinic, space group C2/m, Cm or C2; its unit-cell parameters are: a = 5.463(5), b = 15.865(17), c = 10.825(12) Ǻ, β = 93.7(1)°, V = 936(3) Ǻ3, Z =2. The strongest reflections on the X-ray powder diagram (d, Å-I[hkl]) are: 10.83-13[001]; 5.392-100[002]; 3.281-7[023]; 2.777-7[150]; 2.696-12[004, 201]; 2.524-12[221, 202]; 2.152-8[134, 153]; 1.837-11[135, 173]. Ferrotochilinite is a structural analogue of tochilinite with Fe2+ instead of Mg in the hydroxide part. The type specimen is deposited in Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow.