Abstract

Törnroosite, ideally Pd11As2Te2, is a new mineral species discovered in a heavy-mineral concentrate from the Miessijoki River, Lemmenjoki area, Inari Commune, Finnish Lapland, Finland. It is cubic, space group Fdm (#227), by analogy with isomertieite, a 12.3530(4) Å, V 1885.03 (1) Å3, Z = 8. The strongest six lines of the X-ray powder-diffraction pattern [d in Å (I) hkl] are: 2.182(100)440, 2.376(90)511, 333, 1.544(15)800, 1.862(13)622, 1.2606(13)844, and 1.608(11)731, 553. The associated minerals include sperrylite, Pt–Fe alloy, cooperite, braggite, native Os–Ir–Ru alloy, irarsite, laurite, isomertieite, mertieite II, native Pt, native gold–silver alloy, atokite, Pt–Cu alloy, Cu–Pt–Pd alloy, Cu–Pd–Pt–Au alloy, Pd–Au alloy, along with magnetite, ilmenite, chromite, hematite, columbite–tantalite, tapiolite, garnet, monazite, zircon, pyrite, rutile, uraninite–thorianite, galena, and a mineral of the wolframite series. Törnroosite is black, opaque with a metallic luster, with a silvery black streak. The mineral is isotropic with a yellowish white color in comparison with sperrylite. The reflectance values in air for the standard COM wavelengths are: 45.4 (470 nm), 51.0 (546 nm), 54.1 (589 nm) and 57.45% (650 nm). The calculated density is 11.205(1) g/cm3 (for the empirical formula and unit-cell parameter refined from powder data). The electron-microprobe analyses gave, on average, Pd 72.04, Pt 1.75, Sn 2.13, Sb 0.85, As 8.77, Te 13.15 and Bi 0.79, total 99.48 wt.%, which corresponds to (Pd10.85 Pt0.14)∑10.99(As1.88Sb0.11)∑1.99(Te1.65Sn0.29Bi0.06)∑2.00, based on a total of 15 atoms per formula unit. The average micro-indentation hardness (VHN25) is 519 (n = 4), corresponding to a Mohs hardness of 5. The mineral is named after Professor Ragnar Törnroos, University of Helsinki, Finland.

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