Ion-exchange equilibria between a 2molal aqueous Mg-Fe chloride solution and synthetic olivines, orthopyroxenes, orthoamphiboles and talcs have been experimentally bracketed between 450° and 800°C and between 1 and 4kb. Additional experiments at lower chloride molalities reveal that the distribution coefficient measured is dependent upon chloride concentration. Thermodynamic modelling of the chloride solution, assuming ideal mixing of Mg and Fe species, qualitatively reproduces this behavior if the Mg and Fe species have contrasting dissociation constants. Internally consistent thermodynamic properties of all four minerals and the 'delta' properties of a hypothetical associated electrolyte solution are calculated through a combination of linear programming and least-squares optimization while simultaneously considering constraints provided by calorimetry, net-transfer equilibria and other ion-exchange data. Adequate correspondence between thermodynamic model and the data cannot be attained without allowing the mixing of Mg and Fe in the chloride solution to be non-ideal. Qualitative constraints on the chloride 'excess' properties allow a preliminary estimate of the solid solution properties to be made. All solid solutions are modelled with a symmetric Margules formulation. The resulting olivine WG function has a value near 7kJ at 400°C and drops asymptotically toward zero at high temperatures. The orthopyroxene WG is approximately zero at 400°C and drops toward -3kJ at high temperatures. A 'microscopic' orthopyroxene solution model is formulated to be simultaneously consistent with this bulk excess free energy and with measured M1-M2 site distributions. The single WG value (0.58kJ) calculated for the anthophyllite solid solution is qualitatively consistent with fractionation of Fe into M4. The talc solid solution cannot be constrained to be different from ideal by the data presented here. At present, ion-exchange experiments with Mg-Fe chloride solutions can only be used to compare mineral properties due to uncertainties in dissociation constants and 'excess' properties for the aqueous solution. The role of such uncertainties in the data analysis indicates that solid solution properties derived from previous aqueous chloride ion-exchange experiments must be considered suspect until the properties of each pertinent aqueous electrolyte solution have been examined. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

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Graduation date: 2004

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 121-129).

<p> Fo. determinative curves for lattice planes (301), (311), and (401) were calculated from four natural olivines. 2θ values for each olivine were computed from the lattice parameters using the reciprocal lattice d* for the orthorhombic crystal system d*hkl = [h^2/a^2 + k^2/b^2 + l^2/c^2]^1/2 combined with the Bragg equation λCuKα = 2 sin θhk / d*hkl </p> <p> XRD patterns for 10 natural olivines were used to determine their respective Fo. composition. Errors were calculated for the Fo. composition of the natural olivines yielding an accuracy from the determinative curves of± 6 wt. % Fo. An olivine of 90 wt. % Fo. was X-rayed and plotted along the determinative curves giving values of Fo. composition for (301), (311) and (401) of 89, 87 and 85 wt. % respectively.</p> <p> The effect of Ni, Mn and Ca substituting into the (Mg, Fe) olivine structure causing Δ2θ shifts was also considered and found to be negligible for natural (Mg, Fe) olivines.</p> / Thesis / Bachelor of Science (BSc)

Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Microfiche copy available in Archives and Science. / Bibliography : leaves 86-91. / M.S.

Single crystal X-ray intensity data were collected for four compositionally-intermediate olivine and humanities and their crystal structures were refined by full-matrix, least-squares techniques to investigate cation ordering. Forsterite from Langban, Sweden [(Mg₀.₅₁₉Mn₀.₄₈₂Ca₀.₀₀₃Fe₀.₀₀₁)₂SiO₄, Pbnm, a = 4.94(2) b = 10.419(4), c = 6.123(2)A] was refined to R=0.029 (R_W=0.028) using 731 unique structures factors with F_obs > ^2σFobs. The mean Si-O distance is 1.637A. Site refinements yielded Mg/(Mg+Mn) ratios of 0.92 in the M(2)0₆ octahedron (<M-0> = 2.209A) and a distribution coefficient (K_D) of 0.011. Tephroite from Madagascar [(Mn₀.₈₉₀Mg₀.₀₉₀Fe₀.₀₁₃Ca₀.₀₀₇)₂SiO₄, Pbnm, a = 4.879(2) b = 10.419(4), c = 6.234(2)A] was refined to R = 0.038 (R_W=0.049) using 773 structure factors. The mean si-0 distance is 1.640A. Site refinement yielding Mg/(Mg+Mn) ratios of 0.17 in the M(1)0₆ octahedron (<M-0> = 2.185A) and 0.00 in the M(2)0₆ octahedron (<M-0> = 2.227A) and a K_D of 0.00. Alleghanyite from the Sterling Mine, Ogdensburg, New Jersey [(Mn₀.₅₆₈Mg₀.₃₉₀Zn₀.₀₃₇Ca₀.₀₀₁)₅(F,OH)₂, P2₁/b, a = 4.815(2), b=10.574(3), c=9.083(3)A, α=108.74(2)°] was refined to R = 0.048 (R_W=0.053) using 1873 structures. The mean Si-0 distance is 1.629A. Site refinement with Zn assigned to M93) yielded Mg/(Mg+Mn) ratios of 0.14 in the M(1)0₆ octahedron (<M-0> = 2.212A). The M(3)0₄(F,0H)₂ site (<M-0> = 2.118A) is occupied by the 0.81 Mg, 0.10 Mn and 0.09 Zn atoms. Manganhumite from Langban, Sweden [(Mn₀.₆₈Mg₀.₃₀Fe₀.₀₁Ca₀.₀₁)₇ (Si0₄)₃(OH)₂, Pbnm, a = 4.815(1), b = 10.580(2), c=21.448(5)A] was refined to R = 0.051 (R_W = 0.081) using 1562 structures factors. Mean Si-0 distances for the isolated tetrahedra are <Si(1)-0> = 1.62A and <Si(2)-0> = 1.632A. Site refinement yielded Mg/(Mg+Mn) ratios of 0.30 in the M(1)0₆ octahedron (<M-0> = 2.222 and 2.206A), and 0.75 in the M(3)0₄ (OH)₂ octahedron (<M-0> = 2.117A). Mean octahedral bond distances are positive linear functions of effective ionic radii calculated from the refined site occupancies and f, one-half the number of fluorine atoms per formula unit times the number to monovalent ligands associated with the octahedron. <M(1)-0> = 1.445 + 0.9172 <r_M(1)> <M(2)-(O,OH,F)> = 1.541 + 0.8185 <r_M(2)> - 0.01649 f <M(3)-(O,OH,F)> = 1.502 + 0.8386 <r_M(3)> - 0.02122 f Magnesium, manganese and other cations are ordered on the octahedral sites according to size criteria, although ligancy may be the controlling factor where charge balance and crystal-field effects are involved. Characterization of a suite of naturally-equilibrated Mg-Mn olivines, from Langban, Sweden by electron probe microanalysis, X-ray powder diffraction and infrared spectroscopy and comparison with data in the literature for synthetic specimens demonstrate those unit cell parameters and infrared band positions are nonlinear functions of composition for ordered samples and that nonlinearity increases with the degree of order but that calculated specific gravity is a linear function of composition. / Ph. D.

¡@¡@Igneous activity of Taiwan in Miocene mainly were concentrated in the area north of Miaoli. Nanman is one of the basalt in southern of Taiwan that had been studied by OM, XRD, SEM/EDS and TEM. The rock type is alkali basalt with phenocryst of augite and olivine. The primary minerals include olivine + augite + plagioclase + Anorthoclase + apatite +titanomagnetite + illmenite, and secondary minerals are chlorite + smectite + calcite ¡Ó gypsum.Alteration of Nanman basalt was take placed in mixture and crack of olivine, other minerals are almost fresh. The main replacement are chloritic minerals shown five occurrence types : (1) replaced mixture, (2) vein center of olivine crack, (3) vien of olivine, (4) fibrous and (5) mica-like clay between vein and residual olivine. Each types has clear grain boundary. It¡¦s mean they are not gradual. (4) and (5) are smectite with anomaly composititon. It cause by lack of Al resource, and smectite occurred far from the crack that element do not easily move. Thus, smectite replaced olivine often showed Al-poor and excess Mg. Si/(Si+Al) and Fe/(Fe+Mg) in smectite is positive correlation. This may be considered the moving ability of elements. Composition of (1), (2) and (3) are chlorite/smectite. However there is no observed mixed-layer minerals in XRD. According to TEM , they are chlorite + smectite. Chlorite within abundant of dehydrated cracks could be a evidence of smectite. Because of mixed chlorite and smectite, the correlation between Si/(Si+Al) and Fe/(Fe+Mg) is negative. Different occurrences lead to different mineral, suggest water/rock ratio is an important control factor. High rock/water ratio trend to form chlorite, and low rock/water ratio prefer to form smectite. According to all the results, the steps of altered olivine are first forming chlorite at mixture and olivine cracks. Then, the residual olivine becomes smectite with poor Al and excess Mg, when the rock was cooling down.

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