Acta Crystallographica Section A · 1968 · 107 citations · 0 references
Natural SciencesEarth SciencesGeologyCrystal StructureMineralogyPhase TransformationsCrystal SystemsGrain Structure FormationPhase AnalysisPhase EquilibriaPhase TransitionsThermodynamics Of Phase EquilibriaCrystal Lattice TheoryFeldspar MineralsMonoclinic LatticesMonoclinic SystemPhase BoundariesPhase Boundary EnergeticsTriclinic SystemTwinning
A general theory of grain and phase boundaries (the O-lattice theory) is further developed and tested on alkali feldspars with exsolution lamellae, since measurements exist for the structures of the two-phase system (perthitic feldspars) as well as for the orientation of the phase boundary. It is shown that in this case the adaptation of two monoclinic structures is energetically preferable to the adaptation of a monoclinic and a triclinic one. The phase boundary energy is markedly lower in the former case. Thus, a pseudo-monoclinic structure is produced out of the triclinic by periodic submicroscopic twinning. The calculated orientation of the phase boundary is in close agreement with the measurements.