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Title: The stability of sodalite in the system NaAlSiO sub 4 -NaCl

The reaction sodalite = {beta}-nepheline + NaCl (s) was reversed in solid-medium apparatus and the reaction sodalite = carnegieite + NaCl (l) was reversed at 1 bar (1,649-1,652 K). The experimental reversals between 923 K and 973 K can be fit with a dP/dT of {minus}11 bar/K, suggesting that the excess entropy for sodalite is present only above 923 K. A phase diagram for the NaAlSiO{sub 4}-NaCl system that is consistent with the measured thermochemical data and the experiments between 973 and 1,650 K can be generated if the 61.7 J/mol{center dot}K entropy contribution is included in the S{sup 0}{sub 298} of sodalite. This entropy contribution must be removed below 973 K for the experiments to fit with calculations. Previously unreported thermodynamic data estimated in this study are {Delta}G{sup 0}{sub 298} for sodalite ({minus}12,697 kJ/mol) and carnegieite (NaAlSiO{sub 4}) ({minus}1,958 kJ/mol), S{sup 0}{sub 298} of carnegieite (129.6 J/mol{center dot}K) and compressibility of NaCl{sub liquid} (V{sup P}{sub 298} (cm{sup 3}) = 31.6{center dot}(1 - 24.7{center dot}10{sup {minus}3}{center dot}P + 800{center dot}10{sup {minus}6}{center dot}P{sup 2}))(T in K; P in kbar). Sodalite is a high-temperature, low-pressure phase, stable well above the solidus in sodic silica-undersaturated magmas enriched in NaCl, and its presence constrainsmore » NaCl activities in magmas. Estimates of minimum NaCl (l) activities in the Mont St-Hilaire sodalite syenites are 0.05 at 1,073 K and 0.13 at 1,273 K. Density calculations are consistent with the field observations that sodalite phenocrysts will float in a nepheline syenite liquid. This explains the enrichment of sodalite in the upper levels of the sodalite syenites at Mont St.Hilaire and elsewhere.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4]
  1. (Carnegie Institution of Washington, DC (USA))
  2. (Northwestern Univ., Evanston, IL (USA))
  3. (S.U.N.Y., Stony Brook, NY (USA))
  4. (Univ. of Michigan, Ann Arbor (USA))
Publication Date:
OSTI Identifier:
7017995
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geochimica et Cosmochimica Acta; (USA); Journal Volume: 53:8
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; IGNEOUS ROCKS; SILICATE MINERALS; METAMORPHIC ROCKS; PHASE STUDIES; STABILITY; THERMODYNAMIC ACTIVITY; CHEMICAL COMPOSITION; ENTROPY; GEOCHEMISTRY; INCLUSIONS; MAGMA; PHASE TRANSFORMATIONS; PRESSURE EFFECTS; REACTION KINETICS; ROCK-FLUID INTERACTIONS; SALINITY; SODIUM CHLORIDES; TEMPERATURE EFFECTS; ALKALI METAL COMPOUNDS; CHEMISTRY; CHLORIDES; CHLORINE COMPOUNDS; HALIDES; HALOGEN COMPOUNDS; KINETICS; MINERALS; PHYSICAL PROPERTIES; ROCKS; SODIUM COMPOUNDS; THERMODYNAMIC PROPERTIES 580000* -- Geosciences