The structure of ordered and disordered lead feldspar (PbAl₂Si₂O₈)

Abstract

Other| December 01, 1996 The structure of ordered and disordered lead feldspar (PbAl2Si2O8) Piera Benna; Piera Benna Universita di Torino, Dipartimento di Scienze Mineralogiche e Petrologiche, Turin, Italy Search for other works by this author on: GSW Google Scholar Mario Tribaudino; Mario Tribaudino Search for other works by this author on: GSW Google Scholar Emiliano Bruno Emiliano Bruno Search for other works by this author on: GSW Google Scholar American Mineralogist (1996) 81 (11-12): 1337–1343. https://doi.org/10.2138/am-1996-11-1205 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 Piera Benna, Mario Tribaudino, Emiliano Bruno; The structure of ordered and disordered lead feldspar (PbAl2Si2O8). American Mineralogist 1996;; 81 (11-12): 1337–1343. doi: https://doi.org/10.2138/am-1996-11-1205 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 The Ai-Si configuration in ordered and disordered lead feldspar (PbAl2Si2O8) has been investigated by single-crystal X-ray diffraction. Single crystals synthesized from melt and cooled from T = 1280 to 1000 °C in 1 h and then to T = 700 °C in 15 h show a completely disordered Al-Si configuration with no b-type superstructure reflections (C2/m, a = 8.428, b = 13.054, c = 7.174 Å, β = 115.32°; R = 5.8%). Subsequent structure refinement of a crystal hydrothermally annealed at T = 500 °C and PH2O = 2 kbar for 216 h shows an ordered Al-Si configuration (I2/c, a = 8.388, b = 13.067, c = 14.327 Å, (β = 115.19°; R = 4.7%; Qod ≈ 0.9; 950 b reflections with F0 ≥ 4σ. In the ordered lead feldspar the Pb polyhedron is significantly distorted in comparison with the Sr polyhedron in strontium feldspar. The coordination of the Pb site is reduced from sevenfold, as in strontium feldspar, to a rather irregular sixfold configuration. Such distortion could be related to the lone-pair effect in Pb2+. In the disordered lead feldspar the Fourier map shows an anomalous elec-tron-density distribution around the Pb site and consequently a split-site model for Pb was assumed in the refinement (Pb-Pb′ split = 0.557 Å). 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.