Thermodynamics of order-disorder in minerals; II, Symmetric formalism applied to solid solutions

Abstract

Other| December 01, 1996 Thermodynamics of order-disorder in minerals; II, Symmetric formalism applied to solid solutions Tim Holland; Tim Holland University of Cambridge, Department of Earth Sciences, Cambridge, United Kingdom Search for other works by this author on: GSW Google Scholar Roger Powell Roger Powell University of Melbourne, Australia Search for other works by this author on: GSW Google Scholar American Mineralogist (1996) 81 (11-12): 1425–1437. https://doi.org/10.2138/am-1996-11-1215 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 Tim Holland, Roger Powell; Thermodynamics of order-disorder in minerals; II, Symmetric formalism applied to solid solutions. American Mineralogist 1996;; 81 (11-12): 1425–1437. doi: https://doi.org/10.2138/am-1996-11-1215 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 thermodynamics of order-disorder in mineral solid solutions are handled with symmetric formalism, whereby the mineral is treated as a solid solution between an independent set of end-members with which the range of composition and states of ordering of the phase can be represented. An n-component mineral, requiring s independent order parameters to represent the state of order in the mineral, involves an independent set of n + s end-members. Symmetric formalism involves ideal mixing-on-sites with regular-solution activity coefficients. It is applied to omphacite, orthopyroxene, ferromagnesian cli-noamphibole, and alkali feldspar. The model for omphacite, with a single order parameter, successfully produces the topology of paired miscibility gaps with tricritical points at their apices and with a critical curve connecting them. Ferromagnesian orthopyroxene is shown to behave effectively as an ideal solution at all geologically relevant temperatures. Cum-mingtonite-grunerite solid solutions are slightly positively nonideal in either a two-site or a three-site model. Na-K alkali feldspars with order-parameter coupling involving tetrahedral site occupancies can show the essential topologic relationships in this system, with only one independent binary interaction energy. The power of symmetric formalism comes from the simplicity of its representation of the thermodynamics of minerals and its flexibility with few adjustable parameters. 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.