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

Journal Article · Tue Aug 01 00:00:00 EDT 1989 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(89)90315-3· OSTI ID:7017995

Sharp, Z D ^[1]; Helffrich, G R ^[2]; Bohlen, S R ^[3]; Essene, E J ^[4]

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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)

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 constrains 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.

• OSTI ID: 7017995
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 53:8; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ALKALI METAL COMPOUNDS
CHEMICAL COMPOSITION
CHEMISTRY
CHLORIDES
CHLORINE COMPOUNDS
ENTROPY
GEOCHEMISTRY
HALIDES
HALOGEN COMPOUNDS
IGNEOUS ROCKS
INCLUSIONS
KINETICS
MAGMA
METAMORPHIC ROCKS
MINERALS
PHASE STUDIES
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
PRESSURE EFFECTS
REACTION KINETICS
ROCK-FLUID INTERACTIONS
ROCKS
SALINITY
SILICATE MINERALS
SODIUM CHLORIDES
SODIUM COMPOUNDS
STABILITY
TEMPERATURE EFFECTS
THERMODYNAMIC ACTIVITY
THERMODYNAMIC PROPERTIES