The crystal structures of two pyroxene polymorphs of ZnSiO3 and the orthopyroxene of ZnMgSi206 have been studied. The monoclinic ZnSiO3 crystallizes in the space group C2/c with a= 9"787, b= 9-161, c= 5.296/~, fl= 111.42 °, Z= 8; orthorhombic ZnSiO3, Pbca, a= 18.204, b= 9.087, c= 5.278 A, Z= 16 and orthorhombic ZnMgSi206, b= 8.916, c= 5.209/~, Z= 16. In the structure of the monoclinic ZnSiO3, Zn atoms are coordinated octahedrally (at M1 sites) and tetrahedrally (at M2 sites). The Zn atoms at the M2 sites are not coordinated by the bridging oxygen [0(3)] of the SiO3 chains. In the orthorhombic ZnSiO3, however, Zn atoms at the M2 sites have an irregular octahedral coordination including 0(3) atoms. Because of the difference in coordination of 0(3) to Zn atoms, the shape of the SiOa chains in the two polymorphs of ZnSiOa is different. The structure of the orthorhombic ZnMgSi206 is intermediate between that of enstatite (MgSiO3) and the orthorhombic ZnSiO3. Zn atoms are partially ordered in M1 and M2 sites with site occupancies of 36 and 64% respectively.
CRYSTAL STRUCTURES OF PYROXENE-TYPE ZnSiOa AND ZnMgSi206Lorentz and polarization effects. No absorption correction was made because of the small sizes of the crystal specimens. FACOM 230-60 at the University of Kyoto and NEAC 700 at Osaka University were used for the computations of the structure deterrr, ination and the refinements. The latter were carried out by the fullmatrix least-squares method with ORFLS The structure of 1-phenylcyclopentanecarboxylic acid, C12H1402, has been determined by analysis of 824 diffractometer-measured X-ray reflections and refined by least-squares calculations to an R of 0.066. The crystals are monoclinic, space group P21/c, Z=4, a=6.009, b--6.781, c=24.976 A, fl= 92.08 °. The cyclopentane ring is rigid with a conformation intermediate between the C2 and Cs forms.