Open AccessJournal Article
Volume behavior of silicate solid solutions
Robert C. Newton,Bernard Wood +1 more
TLDR
The S shape of the molar volume curve for binary silicate solid solutions is Sshaped, rather than linear or near-linear as discussed by the authors, and the region of negative deviation from linearity is always close to the small-volume end-member, with positive departures near the large volume end.Abstract:
The characteristic form of the molar volume curve for binary silicate solid solutions is Sshaped, rather than linear or near-linear. The region of negative deviation from linearity is always close to the small-volume end-member, with positive departures near the large-volume end. A Non-Equivalent Site (NS) type of volume behavior is a broad sigmoid that arises from the presence of some crystallographic sites in a structure larger than others capable of accepting the same large substituting cation(s). Initial substitution of the large-volume component into the smaller-volume end-member has only a small efect on the unit-cell volume until the large "easy" sites are saturated, which occurs at a rational mole fraction. Then a region of positive excess volumes follows more or less abruptly. Examples are (Na,K) nephelines and (Mg,Fe'?*) amphiboles. An Equivalent Sr'te (ES) volume behavior occurs in systems where, because of nearly identical sites accepting a certain substituting cation, there are no preferred "easy" sites. The fust small substitution of the larger-volume component produces only local deformations without expansion of the structure as a whole, giving rise to a sharply-curving region of negative excess volume, usually within ten mole percent of the small-volume end-member. Examples are the (Fe'?*,Ca) and (Mg,Ca) garnets, and, probably, the alkali feldspars and olivines. The volume sigmoid is less common among non-silicates. It is shown by some oxide systems, e.g. (Mg,Fe'z*) ilmenites (ES) and magnetite-ulv<ispinel (NS). Thermodynamic excess quantities such as excess entropy, enthalpy, and free energy may be closely related to the volume curves. Possible examples are excess entropy in high alkali feldspars and excess free energy in (Fe'z*,Ca) garnets.read more
Citations
More filters
Journal ArticleDOI
An enlarged and updated internally consistent thermodynamic dataset with uncertainties and correlations: the system K2O–Na2O–CaO–MgO–MnO–FeO–Fe2O3–Al2O3–TiO2–SiO2–C–H2–O2
Tim Holland,Roger Powell +1 more
TL;DR: In this paper, a revised and much enlarged version of the thermodynamic dataset given earlier (Holland & Powell, 1985) is presented, which includes data for 123 mineral and fluid end-members made consistent with over 200 P-T-XCO2-fO2 phase equilibrium experiments.
Book ChapterDOI
Thermodynamics of the Garnet—Plagioclase—Al2SiO5—Quartz Geobarometer
R. C. Newton,H. T. Haselton +1 more
TL;DR: The development of mineralogic geobarometry of crustal metamorphic assemblages has lagged far behind mineralogical geothermometry as discussed by the authors, which is still in the conceptual stage, either lacking an underpinning of experimental or thermodynamic calibration or beset with as yet unresolved experimental difficulties, such as the H2O content of cordierite and its debated effects on the Cordierite-garnet partitioning geobarometer.
Journal Article
Crystal structure and cation distribution in titanomagnetites (Fe (sub 3-x) Ti x O 4 )
TL;DR: In this article, a systematic study of the crystal structure of titanomagnetites was undertaken to characterize the effects of composition and quenching temperature on the cation distribution.
Journal ArticleDOI
Vibrational spectroscopy of end-member silicate garnets
Anne M. Hofmeister,A. Chopelas +1 more
TL;DR: In this article, the authors used factor group analysis and correlating the bands by their intensities to assign the SiO4 internal motions, as a rotation, or to a type of translation.
Journal Article
Static lattice energy minimization and lattice dynamics calculations on aluminosilicate minerals
TL;DR: In this article, a lattice energy minimization and lattice dynamics calculations for the minerals andalusite, sillimanite, kyanite, diopside, cordierite, gehlenite, leucite, orthozoisite, grossular and pyrope are compared with experimental data and previous calculations.
References
More filters
Journal ArticleDOI
Phase relations involving sphalerite in the Fe-Zn-S system
Paul B. Barton,Priestley Toulmin +1 more
TL;DR: In this paper, the Fe-Zn-S was studied from 850 degrees C (appearance of sphalerite-wurtzite polytypes) to 580 degrees C with control of sulfur fugacity.
Journal ArticleDOI
Thermochemistry of high pressure garnets and clinopyroxenes in the system CaO-MgO-Al2O3-SiO2
TL;DR: In this paper, the enthalpies of solution of several synthetic garnets on the join Mg 3 Al 2 Si 3 O 12 (pyrope-grossular) and of several synthesized clinopyroxenes on the joins CaMgSi 2 O 6 -CaAl 2 SiO 6 (diopside-Ca-Tschermak's molecule) were measured in a melt of composition 2PbO · B 2 O 3 at 970 K.
Journal ArticleDOI
Statistical thermodynamic models for ideal oxide and silicate solid solutions, with application to plagioclase
Derrill M. Kerrick,L.S. Darken +1 more
TL;DR: In this article, the authors derived activity composition relations for ideal substitutional solid solutions through the Helmholtz free energy expressed in terms of the partition function, and derived ideal activity expressions for solid solutions of albite and anorthite.