G. Giuseppetti

The crystal structure of eudialyte

As a result of the present paper, the most probable formula unit of eudialyte is: (Fe2+, Fe3+, Mn, Mg)3Zr3(Zr, Nb) x (Ca, R.E.)6Na12[Si9O27−y (OH) y ]2[Si3O9]2Cl z withx=0.1−0.9;y=1−3;z=0.7−1.4. Space group:R

The crystal structure of 2O brittle mica: Anandite

\bar 3

The crystal structure of sarkinite, Mn2AsO4(OH)

a;a=14.244 A,c=30.080 A,Z=3. The crystal structure was determined from 3-dimensional Weissenberg data by Patterson- and electron density-syntheses, and refined by the least squares method:R=0.075 for 831 obs. reflections. Eudialyte is a cyclosilicate with both threefold and ninefold rings of SiO4-tetrahedra. Si−O distances measure 1.62–1.65 A (for shared oxygens) and 1.58–1.60 A (for unshared oxygens). Zirconium has a practically regular octahedral coordination (Zr−O=2.07–2.08 A), whereas iron is surrounded by only four oxygens in a square arrangement (Fe−O=2.04 A); the coordination polyhedron of calcium is a distorted octahedron (Ca−O=2.33–2.38 A). Two non equivalent sodium atoms have rather irregular coordinations: Na(1) is bound to six oxygens which form a fairly distorted hexagonal ring (Na−O=2.53–2.66 A), whereas Na(2) has four shorter distances to three oxygens (Na−O=2.53–2.57 A) and one chlorine (Na−Cl=2.98 A), and three longer distances to oxygens (Na−O=2.74–2.77 A) in a sort of distorted octahedron with a centered face. Some of the most reliable chemical analyses are reexamined in order to derive a formula unit consistent with the crystal structure and to confirm some of its peculiar features, e.g. the presence of two sets of crystallographic sites only partially occupied by chlorine and zirconium atoms respectively.

Reexamination of the crystal structure of phosgenite, Pb2Cl2(CO3)

The crystal structure of weberite, Na2MgAlF7, was redetermined from 3-dim. X-ray data and refined by least squares methods in space groupImma to a conventional reliability factorR=0.036. Mg and Al have octahedral 6-coordination. Two crystallographically independent kinds of Na atoms form different NaF8-polyhedra with the F atoms at the corners of a flattened hexagonal bipyramid and of a square prism, respectively.

Refinement of the crystal structure of northupite: Na3Mg(CO3)2Cl

Anandite has an approximate formula of Ba(Fe3+, Fe2+)3[Si2(Fe3+, Fe2+, Si)2O10−x(OH)x] (S, Cl) (OH), withx=0−1, and belongs to the 2 O brittle mica group. It is orthorhombic; space groupPnmn;a=5.468(9) A,b=9.489(18)A,c=19.963(11) A;Z=4.

The crystal structure of sarcolite

The refined lattice parameters of beryllonite are:a=8.178 (3) A,b=7.818 (2) A,c=14.114 (6) A, β=90.00° (2); space groupP21/n,Z=12. Integrated Weissenberg photographs were taken by using CuK α radiation and multiple film packs. The anisotropic refinement of the crystal structure by means of least-square methods gave a finalR value of 0.063 for the 1388 observed reflections. In the crystal structure PO4 and BeO4 tetrahedra, linked by shared oxygen atoms in a three-dimensional network, form pseudo-ditrigonal rings perpendicular to theb axis. The independent Na atoms lying in the channels formed by the rings are coordinated as an irregular “nine-cornered” polyhedron and as distorted octahedra.

Neubestimmung der Kristallstruktur des Weberits

Sarkinite is a basic manganese arsenate, Mn2AsO4(OH). The lattice parameters are:a=12.779 (2) A,b=13.596 (2) A,c=10.208 (2) A, β=108°53′ (6′). Space groupP21/a,Z=16. The crystal structure has been solved by direct methods from three-dimensional X-ray diffractometer data and refined by least-squares methods toR=0.052 for 3519 independent reflections. The crystal structure is built up by a three-dimensional framework of MnO4(OH)2 octahedra, MnO4(OH) trigonal bipyramids and AsO4 tetrahedra, as found in wagnerite. Isotypy of sarkinite with triploidite is confirmed.

Die Kristallstruktur des Sarkoliths

Phosgenite, Pb2Cl2(CO3), crystallizes tetragonal witha=8.160(4) A,c=8.883(6) A; space groupP 4/m bm,Z=4. The refinement of 320 crystallographically independent reflections measured on an automatic four-circle diffractometer resulted inR=0.032 (for structure factors).