Abstract

The prediction of refractive index from silicate analyses increases the scope of Mathews' arc fusion method for the determination of fine-grained igneous rocks. This is possible by replacing the specific gravity factor in the classical Larsen (Gladstone) equation by a set of empirically derived coefficients for the major oxides. This yields the new equation where (n) is the refractive index, (n − 1) the refractivity, and (W.F.) the weight fraction of the oxides present. Calculations of (n − 1) values for test samples are precise to ± 0.007 which is about the same as the estimated error at source due to in-homogeneities in the prepared glass.

The refractive index of rock glass is a measure of basicity that provides a ready means of linking microscope observations with chemical composition to assist classification, petrological interpretation, and mapping of volcanic or other aphanitic igneous rocks.

First Page Preview

First page PDF preview
You do not currently have access to this article.