Elastic strain effects in coherent perthitic feldspars

Abstract

For coherent cryptoperthites, the compositions inferred from X-ray spacing curves are incorrect due to elastic distortions of the structure; a method is described for correcting these apparent compositions. This method uses the elastic compliances and stress-free lattice parameters to calculate the change in a * due to the coherency strain, and thus the corresponding compositional correction; this method applies only to cases in which both phases are monoclinic The magnitude of the correction depends on the bulk composition, but is typically on the order of 2 to 10 mol % Or. Compositional corrections calculated using this model are roughly half as large as those obtained using Smith's (1961) less rigorous constant volume method.