Stability and structure of new high-pressure silicate, Na (sub 1.8) Ca (sub 1.1) Si6O14

Abstract

Other| December 01, 1995 Stability and structure of new high-pressure silicate, Na1.8Ca1.1Si6O14 Tibor Gasparik; Tibor Gasparik State University of New York at Stony Brook, Department of Earth and Space Sciences, Stony Brook, NY, United States Search for other works by this author on: GSW Google Scholar John B. Parise; John B. Parise Search for other works by this author on: GSW Google Scholar Bonnie A. Eiben; Bonnie A. Eiben Search for other works by this author on: GSW Google Scholar Joseph A. Hriljac Joseph A. Hriljac Search for other works by this author on: GSW Google Scholar American Mineralogist (1995) 80 (11-12): 1269–1276. https://doi.org/10.2138/am-1995-11-1216 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Tibor Gasparik, John B. Parise, Bonnie A. Eiben, Joseph A. Hriljac; Stability and structure of new high-pressure silicate, Na1.8Ca1.1Si6O14. American Mineralogist 1995;; 80 (11-12): 1269–1276. doi: https://doi.org/10.2138/am-1995-11-1216 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract Preliminary phase relations for the bulk composition Na2O·CaO·5SiO2 were experimentally determined at 8–16 GPa and 950–2300 °C, using a split-sphere anvil apparatus (USSA-2000). The dominant phase at pressures between 8 and 14 GPa was a new compound with the ideal formula Na2CaSi6O14; microprobe analyses suggest vacancies that cannot be resolved by X-ray data, resulting in a composition better expressed as Na1.8Ca1.1Si6O14. Single crystals suitable for structure determination were synthesized at 14 GPa and 1900 °C. Two independent sets of X-ray diffraction data were collected on different crystals from the same batch: one with a conventional diffractometer and the other using imaging plates and a synchrotron X-ray source. The compound crystallizes in space group P321 with a = 7.903(2) and c = 4.595(1) Å. Its structure consists of layers in (001); one is centered at z = 0 and contains the (Ca,Na) and [6]Si sites. The other, centered at z = ½, is a sheet of comer-linked [4]Si tetrahedra composed of open-branched crankshaft vierer chains linked by single tetrahedra. Although the SiO6 octahedra are close to regular, with Si-O = 1.789(2) Å, the two symmetry-independent SiO4 tetrahedra are distorted as a result of underbonding between O atoms bonding outside the sheet, with Sil-O = 1.557(2) and 1.638(2) Å, and Si2-0 = 1.619(1) and 1.648(2) Å. Half-normal probability plots show the positional parameters derived from the two data sets to be statistically equivalent. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.