Monchetundraite, Pd2NiTe2, a new mineral from the Monchetundra layered intrusion, Kola Peninsula, Russia

Abstract

Monchetundraite, Pd2NiTe2 is a new mineral discovered in the the Monchetundra layered intrusion, Kola Peninsula, Russia. It forms euhedral grains (up to about 20 μm) intergrown with kotulskite and pentlandite. Monchetundraite is brittle and has a metallic lustre. In plane-polarized light, monchetundraite is white to creamy pinkish white, strongly pleochroic and strongly anisotropic on prismatic sections with rotations tints of pale blue, orange and olive green; it exhibits no internal reflections. Reflectance values (R1 nd R2) of monchetundraite in air are 44.3% and 45.8% at 470 nm; 48.7% and 50.7% at 546 nm; 51.4% and 53.7% at 589 nm, and 55.6% and 57.5% at 650 nm wavelength. Five electron probe micro-analyser (EPMA) measurements of monchetundraite give a mean composition of Pd 40.04 wt%, Cu 0.72 wt%, Fe 0.27 wt%, Ni 10.58 wt%, S 0.64 wt%, Te 48.20 wt%, total 100.07 wt%, which corresponds to the empirical formula (Pd1.96Cu0.06)∑2.02(Ni0.94Fe0.03)∑0.97 (Te1.97S0.04) ∑2.01 based on a total of 5 atoms. Means of eleven EPMA analyses on the synthetic analogue are Pd 40.85 wt%, Ni 10.78 wt%, Te 48.46 wt%, total 100.09 wt%, which corresponds to Pd2.03Ni0.97Te2.00. The mass density, calculated on the basis of the empirical formula, is 9.45 g/cm3. The mineral is orthorhombic, space group Ibam, with a 6.31111(13), b 11.2469(2) A, c 5.16687(15) A, V 366.75(1) A3 and Z = 4. The crystal structure was solved and refined from the powder X-ray-diffraction data of synthetic Pd2NiTe2. Monchetundraite adopts the crystal structure of synthetic Pd2NiTe2, which was first determined by Pocha et al. (2007) and refined in this study. The strongest lines in the X-ray powder diffraction pattern of synthetic Pd2NiTe2 [d in A (I) (hkl)] are: 2.8117 (100) (040), 2.6190 (33) (211), 2.5835 (32) (002), 2.3000 (41) (141), 2.1874 (39) (231), 2.1189 (22) (150), 2.0993 (22) (240), 1.9024 (52) (042), 1.8411 (26) (321), 1.3263 (32) (181). The mineral is named for the locality, the Monchetundra intrusion, Kola Peninsula, Russia.