TY - JOUR

T1 - The crystal structure of vurroite, Pb20Sn2(Bi,As)(22)S51Cl6

T2 - OD-character, polytypism, twinning, and modular description

AU - Pinto, Daniela

AU - Bonaccorsi, Elena

AU - Balic Zunic, Tonci

AU - Makovicky, Emil

PY - 2008

Y1 - 2008

N2 - The crystal structure of the type specimen of vurroite from Vulcano (Aeolian Islands, Italy) has been solved and refined using single-crystal X-ray diffraction data collected at the Elettra synchrotron facility (Basovizza, Trieste). Vurroite has an OD (order-disorder) structure belonging to the category III of OD structures composed of equivalent layers. The OD-groupoid family (lambda and sigma partial operations) and MDO structures were derived by means of the application of the OD theory. The two theoretically possible polytypes with maximum degree of order (MDO polytypes) have pseudo-orthorhombic metric, with lattice parameters a approximate to 45.6, b approximate to 8.4, c approximate to 54 angstrom, and a approximate to 22.8, b approximate to 8.4, c approximate to 54 angstrom, and space group symmetries P2/d11 and A2/d11, respectively. Only the former polytype (MDO) could be identified in the analyzed crystals. The MDO1 structure was solved and refined to R = 6.26% for 4968 reflections with F-o > 4 sigma(F-o). In the standard C2/c setting of the space group the unit-cell parameters of MDO1 are a = 8.371(2), b = 45.502(9), c = 27.273(6) angstrom, beta = 98.83(3)degrees, V = 10265(4) angstrom(3), Z = 4. Frequent twinning with (001) as the twin plane, together with the occurrence of disordered domains in the structure, was observed. The crystal structure of vurroite contains lozenge-shaped composite rods made of coordination polyhedra of Ph and Sn, interconnected into layers parallel to (010) of the standard monoclinic setting. These layers are separated by ribbons of As and Bi, each in distorted octahedral coordination. The ribbons form wavy, discontinuous double layers of PbS archetype. Lone electron pairs of As and Bi are accommodated in the central portions of the PbS-like layers. The structure of vurroite contains building blocks topologically similar to those found in the zinckenite group and in the structure of kirkiite. It can be considered a box-work structure containing the smallest possible pseudo-hexagonal block in the form of a sole octahedron.

AB - The crystal structure of the type specimen of vurroite from Vulcano (Aeolian Islands, Italy) has been solved and refined using single-crystal X-ray diffraction data collected at the Elettra synchrotron facility (Basovizza, Trieste). Vurroite has an OD (order-disorder) structure belonging to the category III of OD structures composed of equivalent layers. The OD-groupoid family (lambda and sigma partial operations) and MDO structures were derived by means of the application of the OD theory. The two theoretically possible polytypes with maximum degree of order (MDO polytypes) have pseudo-orthorhombic metric, with lattice parameters a approximate to 45.6, b approximate to 8.4, c approximate to 54 angstrom, and a approximate to 22.8, b approximate to 8.4, c approximate to 54 angstrom, and space group symmetries P2/d11 and A2/d11, respectively. Only the former polytype (MDO) could be identified in the analyzed crystals. The MDO1 structure was solved and refined to R = 6.26% for 4968 reflections with F-o > 4 sigma(F-o). In the standard C2/c setting of the space group the unit-cell parameters of MDO1 are a = 8.371(2), b = 45.502(9), c = 27.273(6) angstrom, beta = 98.83(3)degrees, V = 10265(4) angstrom(3), Z = 4. Frequent twinning with (001) as the twin plane, together with the occurrence of disordered domains in the structure, was observed. The crystal structure of vurroite contains lozenge-shaped composite rods made of coordination polyhedra of Ph and Sn, interconnected into layers parallel to (010) of the standard monoclinic setting. These layers are separated by ribbons of As and Bi, each in distorted octahedral coordination. The ribbons form wavy, discontinuous double layers of PbS archetype. Lone electron pairs of As and Bi are accommodated in the central portions of the PbS-like layers. The structure of vurroite contains building blocks topologically similar to those found in the zinckenite group and in the structure of kirkiite. It can be considered a box-work structure containing the smallest possible pseudo-hexagonal block in the form of a sole octahedron.

KW - Faculty of Science

KW - vurroite

KW - twinning

KW - polytypism

KW - OD-theory

KW - crystal structure

KW - Pb-Bi-As sulfosalts

U2 - 10.2138/am.2008.2639

DO - 10.2138/am.2008.2639

M3 - Journal article

VL - 93

SP - 713

EP - 727

JO - American Mineralogist

JF - American Mineralogist

SN - 0003-004X

IS - 5-6

ER -