Ferrovalleriite, 2(Fe,Cu)S · 1.5Fe(OH)2: Validation as a mineral species and new data

• Published in: Geology of ore deposits 2013, Vol.55 (8), p.637-647
• Main Authors: Pekov, I. V., Sereda, E. V., Yapaskurt, V. O., Polekhovsky, Yu. S., Britvin, S. N., Chukanov, N. V.
• Format: Article
• Language: English
• Subjects: Earth and Environmental Science; Earth Sciences; Mineral Resources
• ISSN: 1075-7015; 1555-6476
• DOI: 10.1134/S1075701513080102

Ferrovalleriite, ideally 2(Fe,Cu)S · 1.5Fe(OH) 2 , a layered hydroxide-sulfide of the valleriite group and an analog of valleriite with Fe instead of Mg in the hydroxide block, has been approved by the IMA Commission on New Minerals, Nomenclature and Classification as a valid mineral species. It was found in the Oktyabr’sky Mine, Noril’sk, Krasnoyarsk krai, Siberia, Russia. Ferrovalleriite occurs in cavities of massive sulfide ore mainly consisting of cubanite and mooihoekite. In different cases, it is associated with magnetite, Fe-rich chlorite-like phyllosilicate, ferrotochilinite, hibbingite, or rhodochrosite. Ferrovalleriite forms crystals flattened on [001] (from scaly to tabular; up to 5 mm across and up to 0.3 mm thick), typically split and curved. Occasionally, they are combined into aggregates up to 1.5 × 2 cm. Ferrovalleriite is dark bronze-colored, with a metallic luster and black streak. The Mohs’ hardness is ca . 1; VHN is 35 kg/mm 2 . Cleavage is perfect parallel to {001}, mica-like. Individuals are flexible and inelastic. D (calc) = 3.72 g/cm 3 . In reflected light, ferrovalleriite is pleochroic from yellowish to gray; bireflectance is moderate. Anisotropy is strong, with bluish gray to yellowish beige rotation colors. Reflectance values [ R 1 – R 2 %, (λ, nm)] are: 15.6–16.6 (470), 14.8–20.5 (546), 14.7–22.3 (589), 14.5–24.1 (650). The IR spectrum shows the presence of (OH) groups bonded with Fe cations and the absence of H2O molecules. The chemical composition of the holotype (wt %; electron microprobe, H content is calculated) is as follows: 0.10 Al, 0.03 Mn, 45.31 Fe, 0.07 Ni, 18.29 Cu, 20.37 S, 15.62 O, 0.98 H, total is 100.77. The empirical formula calculated on the basis of 2 S atoms is: Al 0.01 Fe 2.55 Cu 0.91 S 2 (OH) 3.07 = (Fe 1.09 Cu 0.91 ) Σ2 S 2 · (Fe 1.34 2+ Fe 0.12 3+ Al 0.01 ) Σ1.47 (OH) 3.07 . The structure of ferrovalleriite is incommensurate (misfit); two sublattices are present: (1) sulfide sublattice, space group , R 3 m or R 32; the unit-cell dimensions are: a = 3.792(2), c = 34.06(3) Å, V = 424(1) Å 3 and (2) hydroxide sublattice, space group , P 3 m 1 or P 321; the unit-cell dimensions: a = 3.202(3), c = 11.35(2)Å, V = 100.8(3) Å 3 . Together with this main polytype modification with three-layer ( R -cell, Z = 3) sulfide block, the holotype ferrovalleriite contains the modification with one-layer ( P -cell, Z = 1) sulfide block (sulfide sublattice with , P 3 m 1 or P 321, unit cell dimensions: a = 3.789(4), c = 11.35