Abstract
The transformation of an andalusite (Al2O3·SiO2 = A) single-crystal to 3:2-mullite (3Al2O3·2SiO2 = M) and non-crystalline silica (SiO2) was investigated at the (100)A and (010)A faces using electron microscopy. The transformation starts topotactically at the surfaces producing a dense layer of mullite and vitreous silica on the surface and underneath the mullite layer. Next, the reaction proceeds by dissolution of andalusite in the vitreous silica and by diffusional transport of alumina to mullite crystals occasionally nucleated at the dissolving andalusite. Transformation along [100]A proceeds twice as fast as along [010]A, which is explained by the higher stability of the (010)A face against dissolution. Transformation by dissolution and precipitation is one order of magnitude slower than the topotactic transformation along [001]A. The transformation reaction of andalusite to mullite and silica is highly anisotropic. Combining the results along the directions [100]A, [010]A, and [001]A predicts the type of transformation which will take place at an arbitrary andalusite face. Only if the cA axis is oriented more than 80° off the surface normal, will the reaction proceed by the dissolutionprecipitation process, whereas for all other orientations andalusite transforms by the fast topotactic reaction along the cA axis.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Application of new experimental and garnet Margules data to the garnet-biotite geothermometer
- Volumes of mixing in aluminosilicate garnets: Solid solution and strain behavior
- Cerium anomaly and Th/U fractionation in the 1.85 Ga Flin Flon Paleosol: Clues from REE- and U-rich accessory minerals and implications for paleoatmospheric reconstruction
- Os solubility in silicate melts: New efforts and results
- Enstatite-forsterite-water equilibria at elevated temperatures and pressures
- The OH-F substitution in synthetic pargasite at 1.5 kbar, 850 °C
- Uptake of aqueous Pb by Cl-, F–, and OH– apatites: Mineralogic evidence for nucleation mechanisms
- Temperature dependence of the hyperfine parameters of synthetic P21/c Mg-Fe clinopyroxenes along the MgSiO3-FeSiO3 join
- Single-crystal thermometric calibration of Fe-Mg order-disorder in pigeonites
- TEM observations on the P1̄ -I1̄ phase transition in feldspars along the join CaAl2Si2O8-SrAl2Si2O8
- Phase transitions induced by solid solution in stuffed derivatives of quartz: A powder synchrotron XRD study of the LiAlSiO4-SiO2 join
- The transformation of andalusite to mullite and silica: Part I. Transformation mechanism in [001]A direction
- The transformation of andalusite to mullite and silica: Part II. Transformation mechanisms in [100]A and [010]A directions
- Structure and twinning of tetragonal Ca3Mn2Ge3O12 garnet
- The equation of state of lawsonite to 7 GPa and 873 K, and calculation of its high pressure stability
- Boron K-edge XANES of borate and borosilicate minerals
- 113Cd double-resonance NMR as a probe of clay mineral cation exchange sites
- Solid state NMR study of oxygen site exchange and Al-O-Al site concentration in analcime
- Isomorphous substitution effect on the vibration frequencies of hydroxyl groups in molecular cluster models of the clay octahedral sheet
- Molecular modeling of the structure and dynamics of the interlayer and surface species of mixed-metal layered hydroxides: Chloride and water in hydrocalumite (Friedel’s salt)
- VIII(Mg,Fe)0.85VI(Mg,Fe)4IV(Fe,Ge)3O12: A new tetragonal phase and its comparison with garnet
- Rietveld analysis of dicalcium aluminate (Ca2Al2O5) – A new high pressure phase with the Brownmillerite-type structure
- Suredaite, PbSnS3, a new mineral species, from the Pirquitas Ag-Sn deposit, NW-Argentina: mineralogy and crystal structure
- Kozoite-(Nd), Nd(CO3)(OH), a new mineral in an alkali olivine basalt from Hizen-cho, Saga Prefecture, Japan
- Florenskyite, FeTiP, a new phosphide from the Kaidun meteorite
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