X-ray single-crystal diffraction data of margarosanite from the Parker Shaft, North Mine Hill, Franklin, New Jersey were collected using a Bruker-AXS three-circle diffractometer equipped with the Smart-Apex CCD detector. Margarosanite is triclinic, P-1, with unit cell parameters: a = 6.7370(3) Å, b = 9.5295(4) Å, c = 6.6961(3) Å, alfa = 110.185(2)°, beta = 103.048(2)°, gamma = 83.037(2)°, V = 392.63(3) Å3, Z = 2. The new structure refinement performed on 9206 diffraction data in the 2θ range 4 < θ < 107° (R1 = 0.035) improves the crystallographic details of a crystal structure described in the seventies and not further studied up to now. The crystal structure of margarosanite is defined by two different structural layers parallel to (-1 0 1): a Si layer constituted by isolated 3-fold rings of SiO4 tetrahedra and a Ca layer made by dimers of CaO6 octahedra and chains of CaO8 polyhedra interconnected via edge-sharing to form a Ca-polyhedral sheet. Additional edge-sharing chains of distorted 8-fold coordinated Pb polyhedra are also present. The crystallographic comparison between margarosanite and walstromite, the Ba-bearing natural counterpart, has been carried out in order to emphasize that the two minerals are isostructural.
Crystal structure refinement of margarosanite PbCa2Si3O9 and relationship with walstromite BaCa2Si3O9
CALLEGARI, ATHOS MARIA;BOIOCCHI, MASSIMO
2016-01-01
Abstract
X-ray single-crystal diffraction data of margarosanite from the Parker Shaft, North Mine Hill, Franklin, New Jersey were collected using a Bruker-AXS three-circle diffractometer equipped with the Smart-Apex CCD detector. Margarosanite is triclinic, P-1, with unit cell parameters: a = 6.7370(3) Å, b = 9.5295(4) Å, c = 6.6961(3) Å, alfa = 110.185(2)°, beta = 103.048(2)°, gamma = 83.037(2)°, V = 392.63(3) Å3, Z = 2. The new structure refinement performed on 9206 diffraction data in the 2θ range 4 < θ < 107° (R1 = 0.035) improves the crystallographic details of a crystal structure described in the seventies and not further studied up to now. The crystal structure of margarosanite is defined by two different structural layers parallel to (-1 0 1): a Si layer constituted by isolated 3-fold rings of SiO4 tetrahedra and a Ca layer made by dimers of CaO6 octahedra and chains of CaO8 polyhedra interconnected via edge-sharing to form a Ca-polyhedral sheet. Additional edge-sharing chains of distorted 8-fold coordinated Pb polyhedra are also present. The crystallographic comparison between margarosanite and walstromite, the Ba-bearing natural counterpart, has been carried out in order to emphasize that the two minerals are isostructural.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
