Palladothallite, Pd3Tl, a new mineral from the Monchetundra layered intrusion, Kola Peninsula, Russia

Abstract

Palladothallite, Pd3Tl, is a new mineral discovered in the Monchetundra layered intrusion, Kola Peninsula, Russia. Palladothallite occurs in orthopyroxenite with disseminated Ni-Cu-Fe sulfides and in near-surface oxidized ore of an orthopyroxenite unit. In the holotype specimen, the new mineral forms anhedral grains about 1 to 20 μm in size intergrown with bortnikovite (Pt4Cu3Zn). Palladothallite and bortnikovite form a rim around tulameenite (Pt2FeCu), Pt-Pd-Fe-Cu alloys, and Pt-Pd-Fe-Cu “oxides” in a goethite matrix. In plane-polarized light, palladothallite is white, anisotropy was not observed; it exhibits no internal reflections. Reflectance values of palladothallite in air (R' in %) are: 53.9 at 470 nm, 57.1 at 546 nm, 59.4 at 589 nm and 61.7 at 650 nm. Twelve electron probe microanalyses of palladothallite gave an average composition (in wt.%): Pd 59.99, Cu 1.19, Fe 0.35, Ag 1.1, Tl 35.64, Se 0.34, and S 0.09, total 99.67, corresponding to the empirical formula (Pd2.894Cu0.096Fe0.032Ag0.053)∑3.075(Tl0.895Se0.023S0.008)∑0.926 based on four atoms, with the ideal formula Pd3Tl. The density, calculated on the basis of the empirical formula, is 13.04 g/cm3. Palladothallite crystallizes with the same structure as synthetic Pd3Tl, which was solved by Kurtzemann & Kohlmann (2010) from powder neutron diffraction data. Palladothallite is tetragonal, space group I4/mmm, with a 4.10659(9), c 15.3028(4) Å, V 258.07(1) Å3, and Z = 4. Palladothallite crystallizes in the ZrAl3 structure type. The name corresponds to its chemical composition, palladium and thallium.

The Zintl Concept Applied to Intergrowth Structures: Electron‐Hole Matching, Stacking Preferences, and Chemical Pressures in Pd5InAs

“…The transferability of these bonding schemes among the structures hints that analogous pictures can be drawn for other group 10 metalbased compounds. We are looking forward to seeing how similar bonding configurations may be used to unify the broader structural chemistry [13][14][15][16][17] of this family of intermetallic phases.…”

“…In this Article, we will consider the structure of Pd 5 InAs as an instance of such a situation, in which a preferred stacking arrangement reveals key bonding features. This compound represents a broader family of group 10 element-rich intermetallics incorporating AuCu 3 -type units [13][14][15][16][17] and has previously been explored for its potential to host hydrogen. [18] It adopts the Pd 5 TlAs structure type (Figure 1), [19][20][21] in which 1-unit-cell thick slabs of the AuCu 3 type and layers of edge-sharing filled square prisms derived from the PtHg 2 type [22] (or its stacking variant, the fluorite type) [23] alternate along the c direction.…”