Diffusion and diffusive phase transformations in alkali feldspar
Feldspar is the most common mineral in the Earth’s crust. It forms a ternary solid-solution among the Ca- (CaAl2Si2O8, anorthite), Na- (NaAlSi3O8, albite) and K- (KAlSi3O8, K-feldspar) end-members, where the latter two pertain to the alkali feldspar solid-solution. At temperatures above about 600°C, alkali feldspar shows continuous miscibility between the Na- and the K end-members. Towards lower temperatures a solvus opens, leading to lamellar unmixing of Na-rich and K-rich domains during cooling. The resulting microstructures reflect the conditions and mechanisms of crystallization in the deep Earth. In particular, the characteristic size of the exsolution lamellae and the extent of chemical segregation between the lamellae reflect the cooling rates and thus shed light on the dynamics of geological processes. Provided the underlying thermodynamics and diffusion kinetics are known, the evolving exsolution microstructure can be described using Cahn-Hilliard theory. In this presentation cation exchange experiments for determining the thermodynamics, combined tracer- and interdiffusion experiments for calibrating the composition-dependent diffusivity tensor, and exsolution experiments for assessing the strain energy associated with coherent lamellar intergrowth are discussed. In addition, related phenomena such as diffusion mediated fracturing and its links to the ice nucleation activity of feldspar aerosol are addressed..
Prof. R. Abart
Department of Lithospheric Research
|Prof. R. Abart|
|Http||Prof. R. Abart|
|Department of Lithospheric Research|
|University of Vienna|