On parkerite and shandite and the crystal structure of Ni₃Pb₂S₂^*

By quantitative spectrographic analysis parkerite from Sudbury carries 1.5 ∓ 0.1 per cent Pb, giving the composition Ni₃Bi_1.95Pb_0.05S₂. If the composition Ni₃Bi_1.2Pb_0.8S₂ attributed to the original parkerite from Insizwa should be verified, it would be proper to use the name parkerite for the natural equivalent of the isostructural α-phase Ni₃Bi₂S₂ —Ni₃BiPbS₂, of the artificial system, and to distinguish the Canadian and South African examples as bismuthian and plumbian varieties.

Shandite (Ramdohr, 1950) from Trial Harbour, Tasmania, gives the distinctive x-ray powder pattern of pure Ni₃Pb₂S₂, the artificial β-phase which will hold almost no Bi in solid solution. In keeping with a face-centered “cubic” lattice and strong optical antisotropism Ni₃Pb₂S₂ has the following structure (rhombohedral description): R3m; r = 5.565 kX, α=60°; Z=1. Pb i at 0 0 0. Pb ii at $12$$12$$12$⁠. 3 Ni at $12$ 0 0; 0 $12$ 0; 0 0 $12$⁠. 2 S at x x x;