Characteristics of altered labradorite surfaces by SIMS and XPS

Abstract

Altered layers, produced by the reaction of plagioclase (labradorite) with dilute solutions of pH 3.5 and 5.7, form at feldspar surfaces. These layers have been identified using secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS). During reaction, Na, Ca and Al are extracted from, the solid in preference to Si, yielding an altered layer enriched in Si. The thickness and composition of the altered layers are dependent on the pH of the reactant solution. Using the difference in the observed secondary ion intensity (from the SIMS profiles) between the reacted and control samples, the thickness of the altered layers can be estimated. The estimated thickness of these layers ranges from tens of angstroms forpH = 5.7 conditions, up to hundreds of angstroms for pH = 3.5 conditions. Scanning electron microscope (SEM) studies do not show any evidence for the formation of secondary phase(s); however, extensive weathering features ( e.g. etch pits) are present on some of the reacted surfaces.