The crystal structure of veenite
The crystal structure of veenite
Mineralogical Magazine (April 2017) 81 (2): 355-368
- antimony
- arsenic
- Canada
- chemical composition
- crystal structure
- dufrenoysite
- Eastern Canada
- electron probe data
- formula
- Hastings County Ontario
- homology
- lattice parameters
- lead
- Madoc Ontario
- metals
- Ontario
- refinement
- single-crystal method
- space groups
- substitution
- sulfarsenites
- sulfosalts
- unit cell
- X-ray diffraction data
- sartorite
- veenite
The crystal structure of veenite is reported for the first time from a sample from the type locality of Madoc (Ontario, Canada). It has been solved and refined by X-ray single-crystal diffraction on the basis of 4973 observed reflections (with F (sub o) > 4sigma (F (sub o) )) with a final R (sub 1) = 0.0396. Veenite is monoclinic P2 (sub 1) , with unit-cell parameters a = 8.429(2), b = 26.069(5), c = 8.962(2) A, beta = 117.447(2) (super o) . The bulk veenite composition is Ag (sub 0.15) Pb (sub 16.029) Sb (sub 8.836) As (sub 6.99) S (sub 39.95) (for Z = 1) corresponding to N = 4.09 (Me (sub 8N) S (sub 8N) (sub +) (sub 8) , theoretical value is 4.0), with the percentage of the Ag-(As,Sb) substituted end-member only equal to 3.51 mol.%, i.e., a nearly pure Pb-Sb-As sulfosalt. The crystal structure is typical for the N = 4 sartorite homologue, with zig-zag walls of trigonal coordination prisms of Pb which separate slabs of diagonally oriented double-layers populated by Sb and As with partial Pb substitution. Orientation of three-membered crankshaft chains formed by strong (As,Sb) - S bonds on the two surfaces of double-layers differs substantially from that in dufrenoysite, which is a pure Pb-As (N = 4) sulfosalt.